Question

A can do a piece of work in 15 days. how much he works in a day?

Answer 1

A can do a piece of work in 15 days. It means A does (1/15)th of the work in 1 day. So in 8 days he has done (8/15)th of the work. What remains to be done is (7/15)th of the work.

A and B together do (7/15)th of the work in 4 days. It means A and B did (7/60)th of the work in each day.

So A and B do (7/60)th of the work in 1 day while A alone does (1/15)th of the work in a day. So B does (7/60)-(1/15) = (7/60) - (4/60) = 3/60 = (1/20)th of the work in 1 day. So B alone can complete the same work in 20 days.

Answer 2

••A do a piece of work in = 15 days
••so he works in 1 day = 1 ÷15 = 1/15
so, the answer is 1/15