Q) A can do a certain work in the same time in which B and C together can do it. If A and B together could do it in 10 days and C alone in 50 days, then B alone could do it in:

a) 15 days              b) 20 days               c) 25 days                     d) 30 days

Ans:

(A + B)’s 1 day’s work = 1/10

C’s 1 day’s work = 1/50

∴  (A + B + C)’s 1 day’s work = 1/10 + 1/50 = 6/50. …. (i)

Given that A’s 1 day’s work = (B + C)’s 1 day’s work …. (ii)

∴  2 x A’s 1 day’s work = 6/50

∴  A’s 1 day’s work = 3/50

B’s 1 day’s work = 1/10- 3/50 = 2/50 = 1/25

∴ B alone could do the work in 25 days.

Hence, Answer is [C].

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