How many 4-digit numbers can be generated from the digits 1, 2, 3, 4, 5 such that no digit appears more than once, and digit 1 is always somewhere to the left of the digit 2?
You have the answer. Trap Analysis is why the other three were written.
Not a worked solution repeated four times — the specific reasoning error each wrong option was built to reward, and why this one tests execution slip.
See pricing50 are analysed free — try those first.