‘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
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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.
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