Why (E) is right: the negation test
A Necessary assumption 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
The library's new evening hours will increase membership, because working adults will finally be able to visit after work.
Which one of the following is an assumption the argument requires?
- The library will hire additional staff to cover the evening hours.
- No other library in town offers evening hours.
- Library membership fees will not increase.
- Working adults currently have no free time whatsoever.
- Working adults who cannot visit during the day want to join the library. Correct
Why (E) is correct
Use the negation test: deny the answer and see if the argument collapses. Deny (E): working adults who cannot visit during the day do NOT want to join the library. Then evening hours bring in nobody, and the conclusion that membership will increase falls apart.
The argument silently depends on those adults actually wanting memberships. That dependence is what makes (E) necessary. None of the other choices passes this test: the argument survives without extra staff, without being the only late-night library, and without frozen fees.
Why the wrong answers are wrong
(A) Out of scope
Staffing is a practical detail. The conclusion is about membership, and evening hours can increase membership whether or not new staff are hired.
(B) Too strong
The argument does not need a monopoly on evening hours. It only needs some working adults to join because of the new hours.
(C) Irrelevant
The argument never mentions fees. A fee change might matter in real life, but the reasoning as stated does not depend on it.
(D) Too strong
They only need some free time in the evening. 'No free time at all' is far stronger than the argument needs, and it is probably false.
Last updated October 12, 2026