Question

A can do a piece of work in 12 days and B can do the same work in 20 days. They work together for 3 days and then A goes away. In how many days will B finish the work?

Answer 1

A can finish a part of work in 1 day= 1/12
B can finish a part of work in 1 day= 1/20
Part of work they a cand together on 1 day=
1/12+1/20= (5+3)/60= 8/60
They worked for 3 days= 8/60×3 = 8/20
A left.
Remaining work= 1-8/20= 12/20
B will finsh work in = 12/20 ×20= 12 days
Hope it helps☺

Answer 2

In 1 day A can do 1/12 part of work
And,In 1 day B can do 1/20 part of work
In 1 day (A+B)can do 1/12+1/20=2/15
In 3 day (A+B) can do 2/15×3=2/5 pow
Remaining work=1-2/5=3/5pow
So,3/5 pow can be done by B in 3/5÷1/20=12 days