Why (B) is right: using the contrapositive
A Inference explanation from our free library. The question below is original, written for this page. Then the full breakdown: why the right answer is right, and why each wrong answer is wrong.
The question
Anyone who finishes the marathon in under three hours qualifies for the championship. Priya finished in 2:55. Jamal did not qualify for the championship.
Which one of the following can be properly inferred?
- Priya will win the championship.
- Jamal did not finish the marathon in under three hours. Correct
- Jamal finished the marathon after Priya did.
- Anyone who qualifies for the championship finished in under three hours.
- Priya trained harder than Jamal.
Why (B) is correct
The rule is: under three hours goes to qualifies. Jamal did not qualify. If he had finished under three hours, the rule says he would have qualified. He did not, so he did not finish under three hours.
That is the contrapositive, and it is airtight. Choice (D) is the famous trap: it reverses the arrow. Under-three-hours is enough for qualifying, but the premise never says it is the only way. Do not convert a conditional for free.
Why the wrong answers are wrong
(A) Too strong
Qualifying is not winning. The premises say nothing about who wins.
(C) Out of scope
Their times are never compared. Jamal might have finished in 3:05 or not finished at all.
(D) Reversed
The premise says under-three-hours implies qualifies. This flips it. There might be other ways to qualify, like a sponsor exemption. The premise does not rule that out.
(E) Out of scope
Training is never mentioned. Faster times do not prove harder training on these premises alone.
Last updated October 12, 2026