L1[0,1]⊆L2[0,1]
Reasoning mistake
Converse assumed
The theorem runs one way. You used it in the other.
79 wrong options in the bank13 free to read
Would you have fallen for these?
Each is a real option from a previous-year paper. Read it cold and decide before opening it.
- Option B
Why this is wrong, and why it looks right
The reverse fails: f(x) = x−1/2 has ∫01|f|dx = 2, so f∈L1[0,1], but ∫01|f|2dx =∫01x−1dx diverges, so f∈/L2[0,1]. Finite measure only buys containment toward the higher exponent, not both ways.
From this question
Which of the following are true?
Part C · free
- Option C
The p-value is the probability that H0 is true given the observed data.
Why this is wrong, and why it looks right
The p-value is P(data this extreme or more | H0 true) — a probability about the data computed assuming H0, not P(H0 | data). Converting one to the other needs Bayes' theorem and a prior on H0, which the p-value calculation never uses.
From this question
For testing H0:θ=θ0 against H1:θ=θ1 at level α, which of the following are true?
Part C · free
- Option B
−n/∑lnXi
Why this is wrong, and why it looks right
False — this estimates θ, not 1/θ.−n/∑lnXi is the reciprocal of the correct estimator and is in fact the MLE of θ. Reciprocals do not commute with expectation, so an unbiased estimator of 1/θ cannot simply be inverted to give one for θ.
From this question
See the full questionFor n ≥ 2, let X1,…,Xn be a random sample with density f(x|θ)= θxθ−1 on 0<x<1,θ>0 unknown. Which of the following is the UMVUE for 1/θ?
Part B · december 2023 · free
- Option B
G is a cyclic group.
Why this is wrong, and why it looks right
False — 'need not be' is the point. P has order 172 and may be Z17×Z17 rather than Z289, in which case G≅Z7×Z17×Z17 has no element of order 2023. Abelian does not imply cyclic once a prime appears squared; Z7×Z289 is cyclic but it is not the only option.
From this question
See the full questionLet G be a group of order 2023. Which of the following statements are true?
Part C · june 2023 · free
- Option C
f′ is continuous
Why this is wrong, and why it looks right
False: f(x)=x2sin(1/x)(f(0)=0) is differentiable everywhere, but f′(x)=2x sin(1/x)−cos(1/x) for x≠0 oscillates with no limit as x→0, while f′(0)=0 — so f′ is discontinuous at 0 despite having the intermediate value property from option (0).
From this question
Let f:R→R be differentiable. Which of the following are true?
Part C · free
- Option B
Xn→X in probability ⟹ Xn→X almost surely.
Why this is wrong, and why it looks right
This assumes the converse of the true implication in option (a). The classic counterexample is a 'moving window' sequence on [0,1] — indicators of shrinking, cyclically sweeping intervals — which converges to 0 in probability, yet since some window always contains any fixed point, never converges there almost surely.
From this question
Let X1,X2,… and X be random variables on a common probability space. Which of the following implications hold in general?
Part C · free
- Option D
Xn→X in distribution ⟹ Xn→X in probability.
Why this is wrong, and why it looks right
Convergence in distribution only constrains the marginal law of Xn, saying nothing about how Xn and X are jointly related on the same probability space, so it generally can't force |Xn−X|→0 in probability. The implication does hold in the special case where X is almost surely a constant, but not otherwise.
From this question
Let X1,X2,… and X be random variables on a common probability space. Which of the following implications hold in general?
Part C · free
- Option B
(x) is a maximal ideal.
Why this is wrong, and why it looks right
Z[x]/(x)≅Z, which is a domain but not a field, so (x) is prime but not maximal. It sits properly inside the strictly larger ideal (2,x), and primality only coincides with maximality in special rings like PIDs — not in Z[x].
From this question
Consider the ring Z[x]. Which of the following are true?
Part C · free
- Option C
P(diseased | positive) > 1/2.
Why this is wrong, and why it looks right
P(D|+) = 1/6 ≈ 0.167, well below 1/2. The test's high sensitivity and specificity describe P(test | disease), not P(disease | test); with only 1% prevalence, the 4.95% of healthy people who false-positive outnumber the 0.99% of diseased people who true-positive.
From this question
A test for a disease has sensitivity 0.99 and specificity 0.95, and the disease affects 1% of the population. Which of the following are true?
Part C · free
- Option B
If P(A | B) = 1 then P(B | A) = 1.
Why this is wrong, and why it looks right
False, and here the symmetry genuinely breaks. P(A | B) = 1 means P(A ∩ B) = P(B), that is B is contained in A up to null sets. Then P(B | A) = P(B)/P(A), which is less than 1 whenever P(B) < P(A). Containment runs one way only.
From this question
See the full questionLet A, B be two events in a discrete probability space with P(A) > 0 and P(B) > 0. Which of the following are necessarily true?
Part C · june 2023 · free
- Option D
If P(A | B) > P(B) then P(B | A) > P(A).
Why this is wrong, and why it looks right
False. Written out, the hypothesis is P(A∩B)>P(B)2 and the conclusion P(A∩B)>P(A)2, which are different statements. Take B ⊂ A with P(A) = 9/10 and P(B) = 1/10: then P(A | B) = 1 > 1/10 = P(B), so the hypothesis holds, but P(B | A) = 1/9 (verified) and SymPy confirms 1/9 − 9/10 < 0, so the conclusion fails. Compare with (C): the same shape of statement, but comparing against the other event's probability destroys the symmetry.
From this question
See the full questionLet A, B be two events in a discrete probability space with P(A) > 0 and P(B) > 0. Which of the following are necessarily true?
Part C · june 2023 · free
- Option D
If ∇u⋅∇v=0 at every point, then f is an entire function.
Why this is wrong, and why it looks right
False — it is (C) read backwards. Take f(z) = z̄, so u = x and v = −y: SymPy gives ∇u⋅∇v=1⋅0+0⋅(−1)=0, yet f is nowhere holomorphic. Orthogonal gradients are one consequence of Cauchy–Riemann, not equivalent to them.
From this question
See the full questionLet f:C→C be a real-differentiable function and define u(x, y) = Re f(x + iy), v(x, y) = Im f(x + iy). Let ∇u=(ux,uy) denote the gradient. Which one of the following is necessarily true?
Part B · december 2023 · free
- Option D
If (a1+⋯+an)/n converges then (an) converges
Why this is wrong, and why it looks right
False: an=(−1)n has Cesàro means (a1+⋯+an)/n→0, but (an) itself never converges. Cesàro summability only follows FROM convergence, not the other way round.
From this question
Let (an) be a sequence of real numbers. Which of the following are true?
Part C · free
- Option D
If B(v, w) = 0 then either v = 0 or w = 0.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2024
- Option C
B(x, x) ≠ 0 for all nonzero x∈R4.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2024
- Option D
deg h ≥ n for every nonzero h∈kerφ.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2024
- Option A
nowhere
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B
- Option A
All Manuals are Booklets.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part A · june 2025
- Option B
All Catalogues are Booklets.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part A · june 2025
- Option D
All Catalogues are Manuals.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part A · june 2025
- Option A
f is differentiable everywhere and f′ is continuous
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B
- Option D
f is differentiable everywhere and f′ is bounded on [−1, 1] but f′(0) ≠ 0
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B
- Option B
undefined, since the series diverges
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B
- Option C
path-connected but not connected
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B
- Option C
lim(y→+∞) |f′(iy)| =+∞
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2024
- Option B
If F(x) = 0 for all x ∈ [0, 1], then f(x) = 0 for all x ∈ [0, 1].
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2024
- Option C
lim(x→0) f(x,0) = lim(y→0) f(0,y).
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2025
- Option A
8/25
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2025
- Option B
p0>p3
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2025
- Option B
Xn converges to X in probability as n→∞ implies that Xn converges to X almost surely as n→∞.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2024
- Option B
There exists (a,b)∈R2 such that h_(a,b) is not differentiable at t = 0.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2024
- Option C
The function f is differentiable at the point (0, 0).
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2024
- Option C
no professionals are teachers
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part A · december 2025
- Option C
f must be uniformly continuous.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2024
- Option B
If |X| divides n, then G is abelian.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2024
- Option C
population of young people is going to increase with a faster rate in the long run if the same status continues
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part A · december 2025
- Option D
proportion of elderly people is going to decrease in the long run if the same status continues
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part A · december 2025
- Option A
Anwar was the most senior
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part A · december 2025
- Option C
S ~ W12(19,19∑)
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2025
- Option D
G has a subgroup of order 6.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C
- Option D
A4 has a subgroup of order 6
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C
- Option C
(P) is FALSE, (Q) is true.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2025
- Option D
Both (P) and (Q) are FALSE.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2025
- Option B
If an1/n → L then an₊1/an→L
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C
- Option D
(0.95X, X)
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2025
- Option A
1/64
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2025
- Option D
rank A = 2.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2023
- Option B
rank A = 1.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2023
- Option A
Var(β̃1)>Var(β̃2),E(β̃1−β)2>E(β̃2−β)2
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2025
- Option C
The maximum likelihood estimator of θ is min{−2X(1)/3,2X(n)}
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2025
- Option A
Xn→X almost surely
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B
- Option C
f maps an open neighbourhood of (0, 0) in R2 onto an open subset of R3
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · june 2024
- Option A
If A is one-to-one but not onto, then m > n
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · june 2024
- Option B
If A is onto but not one-to-one, then m < n
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · june 2024
- Option D
If A is one-to-one, then m = n
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · june 2024
- Option C
P(Y<1/2)={S(1/2)}4
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2025
- Option D
A is symmetric.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C
- Option A
If A is a real 3×2 matrix and B a real 2×3 matrix with BA =I2, then AB =I3.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2023
- Option A
There is no continuous real-valued function g defined on any interval of R containing 0 such that f(x, g(x)) = 0.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · june 2023
- Option D
u(π)−u′(π)=eπ.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2025
- Option B
S has exactly one element
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · june 2024
- Option B
There exists a holomorphic surjective map f:Ω2→Ω1.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2023
- Option D
There exists a holomorphic injective map f:Ω2→Ω1.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2023
- Option D
y(x)=(1/2)(x2−x+2) is an extremal for J1
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · june 2025
- Option B
Ramesh
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part A · june 2025
- Option C
a is not divisible by 48.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2023
- Option A
f ∘ g (when defined)
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B
- Option C
A is symmetric
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B
- Option B
A is bounded above but not bounded below.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2025
- Option A
There exists a real invertible matrix P such that PAP⁻1 is a diagonal matrix and PᵗP=I3.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2024
- Option D
A has only real eigenvalues and it is not diagonalizable over R.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · december 2024
- Option A
Statement 1
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part A · september 2022
- Option B
H is normal only if G is abelian.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B
- Option D
If |1 − āz| < |z − a|, then |z| < 1
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part B · june 2024
- Option D
If A is diagonalisable then A is invertible
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C
- Option C
There does not exist (s1,s2)∈R2 such that q2(s1,s2)=−5
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · june 2024
- Option D
Suppose that there exists a subspace W of Cn such that T(W)⊆W,Cn=V+W and V ∩ W = {0}. Then there exists a positive integer k such that Tᵏ is the identity map.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · december 2024
- Option B
L1(μ)⊆L2(μ).
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C
- Option B
The preimage of a connected set under p is a connected set.
Why this is wrong, and why it looks right
The option is above and the answer is on the question page, both free. This is the part that is not: the reasoning that makes this particular wrong option feel like the right one.
Part C · june 2025
66 of these are analysed in Trap Analysis
Every wrong option in the paper, analysed. Not a worked solution repeated four times — the specific mistake behind each distractor. The options and the answers stay free.
See pricingThe counterexamples that settle these
One example is enough to kill a false statement. These are the standard ones for the claims above.
- Closed and bounded ⇒ compact
- Bounded ⇒ totally bounded
- Connected ⇒ path-connected
- Continuous on a bounded interval ⇒ bounded
- Uniformly continuous ⇒ Lipschitz
- Differentiable ⇒ continuously differentiable