Question

A and B can complete a work in 15 days and 10 days respectively. They started doing the work together but after 2 days B had to leave and A alone completed the remaining work. The whole work was completed in :?

Answer 1

in 2 days work was completed
=1/6 part of work was completed
part of work to be completed =5/6
in 1 day a can do 1/15 part of work
so 5/6 part of work he can complete in =1÷5/6×1/15=18 days
work was completed in 18+2 days =20 days