Question

A and B together can finish a piece of work in 12 days , if A alone can finish work in 20 days , in how many days B alone can finish it

Answer 1

(A+B)'s 1 day's work = 1/12
A's 1 day's work = 1/20
B's 1 day's work = 1/12 - 1/20
=( 5- 3)/60
= 2/60
= 1/30
Hence B alone can finish the work in 30 days.

Answer 2

A&B is finishing their work in 12 days
So, work of A&B in1 day = 1/12

A can finish work in 20 days
So, work of A in 1 day = 1/20

Now work of B in one day = 1/12-1/20
= 5-3/60
= 2/60
= 1/30
Therefore,
B can finish the work =30*1
= 30 days