Q) A, B and C can do a piece of work in 20, 30 and 60 days respectively. In how many days can A do the work if he is assisted by B and C on every third day?

a) 12 days              b) 15 days             c) 16 days                d) 18 days

Ans:

A’s 1 day work = 1/20

B’s 1 day work = 1/30

C’ 1 day work = 1/60

∴ (A + B + C)’s 1 day’s work = 1/20 + 1/30 + 1/60 = 6/60 = 1/10

∴ work done in 1st 3 days

= 1st day’s work + 2nd day’s work + 3rd day’s work

= 1/20 + 1/20 + 1/10 = 4/20 = 1/5

Since time taken by A to do 1/5 work = 3 days

∴ time taken by A to do full work = 3 / (1/5) = 15 days

Hence, Answer is [B]

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