Question

a can do a piece of work in 12 days. b can do same piece of work in 15 days. after a had worked for 3 days b also join a to finish the remaining work. in how many days work will be finished?

Answer 1

8 days

Explanation:

A can do a piece of work in 12 days, then A can complete 1/12 of the work in 1 day.

B can do a piece of work in 15 days, then B can complete 1/15 of the work in 1 day.

So for 3 days, A can complete 3 x 1/12 = 1/4 of the work in 3 days

when B joins A, they both complete 1/12 + 1/15 = 5/60 + 4/60 = 9/60 = 3/20 of the work in 1 day.

So the work by both A and B = 1 - 1/4 = 4/4 - 1/4 = 3/4 or 15/20

the number of days both A and B will complete: (15/20)/(3/20) = 5 days

So A will work 3 days, then A and B will work the next 5 days for total of 8 days