Question

A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :

Answer 1

1 day's work of A=1/15

1 day's work of B=1/20

1 day's work of A+B= 1/15+1/20 = 7/60

4 day's work of A+B = 4*7/60 = 7/15

Hence remaining work = 1-7/15 = 8/15