A and B can do a piece of work in 12 days while A alone can do it in 20 days. How long will B alone take to finish the work?

A 8days

B 30days

C 32 days

D 50 days

Correct Answer: Option B

In 12 days, A and B can do 1 job.

In 1 day, A and B can do 1/12 job.

Again,

In 20 days, A can do 1 job

In 1 day, A can do 1/20 job

Thus, In 1 day, B alone can do (1/12 - 1/20) job

= (10-6)/120 job

= 4/120 job

= 1/30 job

Now,