Question

A can do a piece of work in 25 days. A and B together can do it in 20 days. How many days would B alone take to do the same work?

Answer 1

One day work of ,
A=1/25
A+B=1/20
so ,B=1/20-1/25
= 5-4/100
=1/100part
so no. of days taken by B to complete the work =(1÷1/100)
=1×100/1
=100 days

Answer 2

A,s one day work = 1/25
B's one day work = x

A and B together can do a work in 20 days.
A's and B'B's one day work = 1/20

1/20-1/25= B's one day work

LCM of 20 and 25 = 100

1/20×5= 5/100
1/25×4=4/100

5/100-4/100
=1/100

do reciprocal

1/100=100/1
=100

B alone can do the work in 100 days.

hope it helps.