(a) 20 days

**(b) 22(1/2) days**

(c) 25 days

(d) 30 days

Explanation:

Ratio of times taken by A and B = 1 : 3.

The time difference is (3 – 1) 2 days while B take 3 days and A takes 1 day.

If difference of time is 2 days, B takes 3 days.

If difference of time is 60 days, B takes (3/2 x 60) = 90 days.

So, A takes 30 days to do the work.

A’s 1 day’s work = 1/30

B’s 1 day’s work = 1/90

(A + B)’s 1 day’s work = (1/30 + 1/90) = 4/90 = 2/45

A and B together can do the work in 45/2 = 22(1/2)

days.