Question

A can do a piece of work in 80 days. He works at it for 10 days and then B alone finishes the work in 42 days. The two together could have completed the the work in how many days ?

Answer 1

A man can finish the work in 80 days. So in 10 days he finshes 10/80 = 1/8 of the work.
So 7/8 of the work is remaining. It means B finishes 7/8 of work in 42 days.
So B can complete the work in 42(8/7) = 48 days, working alone.
Suppose they work together.
A finishes 1/80 of work in 1 day
B finishes 1/48 of work in 1 day.
So together i 1 day they complete (1/80+1/48) of work = 3/240+5/240= 8/240 = 1/30 of work
Hence they can complete the work in 30 days
Answer: 30 days

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