NSW Schools - Math Practice

Problem Statement

An advertisement for a cleaning product claimed:

Quick-Stain Remover never fails to remove a stain.

Four cleaning products were used on bathroom walls, and two questions were asked in each case:

Which two of the missing answers must be known in order to test the truth of the claim in the advertisement?

(a) and (b)

(b) and (d)

(a) and (d)