A is thrice as good a workman as B and takes 20 days less to do a piece of work than B. B alone can do the whole work in:
Explanation:
Ratio of efficiency of A and B = 3 : 1.
We know the ratio of efficiency is reciprocal to the ratio of time taken to complete a certain work.
∴ Ratio of the time taken by A and B = A ∶ B ∷ 1 ∶ 3
Let A takes x days to complete the work, hence B takes 3x days to complete the same work.
⇒ 3x - x = 20
⇒ x = 10
∴ B takes 3 × 10 = 30 days.
Hence, option (c).
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