A and B together can do a piece of work in 10 days. A alone can do it in 30 days. The time in which B alone can do it is :

A and B together can do a piece of work in 10 days. A alone can do it in 30 days. The time in which B alone can do it is :
[A]10
[B]12
[C]20
[D]15

15
(A+B)’s 1 day’s work = \frac{1}{10}
A’s 1 day’s work = \frac{1}{30}
∴ B’s 1 day’s work = \frac{1}{10}-\frac{1}{30}
=\frac{3-1}{30}=\frac{2}{30}=\frac{1}{15}
Hence, B, alone can complete the work in 15 days.

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