# How many days B alone does it work?

A does 80 % of a work in 20 days. He then calls in B and together they finish the remaining work in 3 days. How long B alone would take to do the whole work:

- 23 days
- 37 days
- 75/2 days
- 40 days

**Answer: (3) 75/2 days**

A can 80% of a work = 20 days

Then, the whole work is done by A = 20 x 5/4

= 5 x 5 = 25 days

Remaining work = 1 – 4/5

= (5 – 4)/5 = 1/5

Remaining work done by A and B = 3 days

Then, whole work done by A and B = 3 x 5 = 15 days

A can do the work in a day = 1/25 days

(A + B) can the work in a day = 1/15 days

Then, B can do the work in a day = 1/15 – 1/25

= (5 – 3)/75

= 2/75

Therefore, B can do the whole work = 75/2 days.

Hence, the answer is (3) 75/2 days.