Q) A and B can complete a work in 15 days and 10 days respectively. They started doing the work together but after 2 days B had to leave and A alone completed the remaining work. The whole work was completed in :

a) 8 days                     b) 10 days             c) 12 days                     d) 15 days

Ans:

A’s 1 day work = 1/15

B’s 1 day’s work = 1/10

∴ (A + B)’s 1 day’s work = 1/15 + 1/10 = 5/30 = 1/6

∴ (A + B)’s 2 days work = 2 x 1/6 = 1/3

∴ Balance work = 1 – 1/3 = 2/3

Since Time taken by A to do 1/15 work = 1 day

∴ Time taken by A to do 2/3 work = (2/3)/(1/15) = 10 days

Therefore, total time taken = 2 + 10 = 12 days

Hence, Answer is [C].

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