Question

A can do a work in 15 days and B in 20 days. If they work together on it for 4 days, what fraction of work will be left?

Answer 1

A can do work in 15days so each day A do 1/15th part of total work
similarly each day B do 1/20th part of total work
each day they both together do 1/15+1/20 part
so in 4 days they will do 4(1/15+1/20) part
4(4+3/60)=7/15
work left=8/15

Answer 2

Thank you for asking this question. Here is your answer:

Suppose total work is 1

A=1/15 & B=1/25 for one day work

when both work together

(A+B)= (1/15)+(1/25)=7/60

for 7 days

(7/60)x7=7/15

For remaining work

1-(7/15)=8/15

Answer (8/15)