Question

‘a' can do a piece of work in 80 days. He works at it for 10 days, and then ‘b' alone finishes the remaining work in 42 days. In how much time will ‘a' and ‘b,' working together, finish the work?

a. 40days

b. 30 days

c. 25 days

d. 20 days

Answer 1

Ans. B. 30 days

Work completed by A in 10 days = 10/80 = 1/8

Remaining work = 7/8

B complete 7/8 part in 42 days

So he complete 1 (full) part in 42÷(7/8) = 48 days

So both will complete it in 1 day =(1/80 + 1/48) = 1/30

Hence in 30 days they complete the work.