In a test with multiple choice questions, candidates get 4 marks for a correct answer and lose 1 mark for an incorrect answer. Two candidates A and B attempting 18 and 13 questions, respectively, secure equal marks. How many more INCORRECT answers does A have compared to B?
CSIR NET September 2022 — Part A — General Aptitude
All 13 Part A questions we have transcribed from this paper, of the 13 on the site for this sitting — every option and the answer key, with the reasoning for each one.
Part A
General aptitude. One correct option. 2 marks, −0.5 for a wrong answer, and 15 of the 20 count.
Q1Execution slip
- A.3
- B.4✓
- C.5
- D.6
Solution
If A answers x correctly, A scores 4x − (18 − x) = 5x − 18; B scores 5y − 13. Equal marks give 5(x − y) = 5, so x − y = 1. The gap in incorrect answers is (18 − x) − (13 − y) = 5 − (x − y) = 4.
Q2Execution slip
A ranks 10th from both the top and the bottom in merit among the girls in her class. B ranks 6th from the top and 16th from the bottom among boys in the same class. If A is immediately ahead of B in merit order, her rank in the entire class would be
- A.16th from the top and 26th from the bottom
- B.15th from the top and 26th from the bottom✓
- C.15th from the top and 27th from the bottom
- D.16th from the top and 27th from the bottom
Trap Analysis has the working, and why each of the other options was written to tempt you.
Q3Execution slip
A 360 ml aqueous solution contains 40% alcohol. How much will be the approximate percentage of alcohol if 3600 ml of water is added to the solution?
- A.2.6
- B.3.6✓
- C.4.0
- D.1.0
Solution
The alcohol is 40% of 360 = 144 ml and does not change. The volume becomes 360 + 3600 = 3960 ml, so the concentration is 144/3960 = 40/11 ≈ 3.64%.
Q4Execution slip
If 90 people are to be seated randomly in 15 rows of 6 seats each, what is the probability that a person gets a seat at either end of a row?
- A.1/2
- B.1/4
- C.1/3✓
- D.1/15
Trap Analysis has the working, and why each of the other options was written to tempt you.
Q5Execution slip
Consider the following four statements. Statement 1: “Statement 3 is true.” Statement 2: “Statement 1 is true.” Statement 3: “Statement 1 is true and Statement 2 is false.” Statement 4: “Statements 1, 2 and 3 are false.” Which of the above statements must be true for the four statements to be mutually consistent?
- A.Statement 1
- B.Statement 2
- C.Statement 3
- D.Statement 4✓
Trap Analysis has the working, and why each of the other options was written to tempt you.
Q6Execution slip
On a track of 200 m length, S runs from the starting point and R starts 20 m ahead of S at the same time. Both reach the end of the track at the same time. S runs at a uniform speed of 10 m/s. If R also runs at a uniform speed, then how much more time would R take to run the entire course?
- A.0.5 second
- B.1.0 second
- C.1.5 second
- D.2.2 seconds✓
Trap Analysis has the working, and why each of the other options was written to tempt you.
Q7What the inference means
The arithmetic mean of five numbers is zero. The numbers may not be distinct. Which of the following must be true?
- A.The product of the numbers is zero
- B.At most two of these numbers are positive
- C.There cannot be exactly one zero
- D.There cannot be exactly one non-zero number✓
Trap Analysis has the working, and why each of the other options was written to tempt you.
Q8What the inference means
Of all the English magazines published in a country, magazine M is read by the highest number of readers. It necessarily follows that
- A.M is the most popular English magazine published in the country.✓
- B.M is the most popular English magazine in the country.
- C.M is the most popular magazine in the country.
- D.The study has not considered the readership of English magazines published outside the country.
Trap Analysis has the working, and why each of the other options was written to tempt you.
Q9Execution slip
The number of three digit PINs, in which the third digit is the sum of the first two digits, is
- A.55✓
- B.9
- C.45
- D.11
Solution
A PIN may begin with 0, so the first two digits a and b range over 0–9 subject only to a + b ≤ 9. The number of such pairs is C(11, 2) = 55, and each determines the third digit.
Q10Execution slip
Consider a right angled triangle BAC, right angled at A, with medians CM and BL having the same length, where M is the midpoint of AB and L is the midpoint of AC. The ratio of the length of BC to that of ML is
- A.2✓
- B.3/4
- C.4/3
- D.1
Trap Analysis has the working, and why each of the other options was written to tempt you.
Q11Execution slip
A battalion consists of elephants, horses and soldiers totaling to 3500. There are twice as many horses as elephants and one-fourth of the soldiers are riding these animals. In the stand still position, number of feet on ground is 7500. The number of horses in the battalion is
- A.525
- B.625
- C.550
- D.600✓
Trap Analysis has the working, and why each of the other options was written to tempt you.
Q12Execution slip
The wholesale price per unit of an item is C0 up to first 19 units. The unit price falls by 10% if 20 to 29 units are purchased and by another 10 % if 30 or more units are purchased. If 120 units are bought, the total price paid is approximately
- A.99C0
- B.97C0✓
- C.91C0
- D.81C0
Trap Analysis has the working, and why each of the other options was written to tempt you.
Q13Execution slip
A 5 kg watermelon contains 99% water by weight. Some of the water evaporates and the melon now contains 98% water by weight. What is the weight (in kg) of watermelon now?
- A.4.5
- B.2.5✓
- C.4.8
- D.4.9
Solution
The solid matter is 1% of 5 kg = 0.05 kg and does not evaporate. Afterwards it is 2% of the new weight W, so 0.05 = 0.02 W and W = 2.5 kg. Tracking the part that stays constant, rather than the water, is what makes this tractable.