Discussion
A does 20% less work than B. If A can complete a piece of work in \(7\frac{1}{2}\) hours then B can do it in
Answer: A
A does 20% less work than B, so A's rate is 0.8 of B's. If A takes 7.5 hours, B takes 7.5 x 0.8 = 6 hours, option A.
The other options come from using 1.25 or other wrong factors, such as \(5\frac{1}{2}\), \(6\frac{1}{2}\) and \(6\frac{3}{4}\) hours.
Work is rate times time, so with A's rate at 80 per cent of B's, B takes 80 per cent of A's time. Then 7.5 x 0.8 = 6 hours. The tempting answer of 9.375 hours comes from dividing by 0.8 instead of multiplying, and it is not offered. The other options come from similar slips.
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