131. A works twice as fast as B. If B can complete a work in 12 days independently, the number of days in which A and B can together finish the work in :

✅ The correct answer is option A.
Ratio of rates of working of A and B = 2 : 1.
So, ratio of times taken = 1 : 2.

B’s 1 day’s work =
1
.

12

A’s 1 day’s work =
1
; (2 times of B’s work)

6

(A + B)’s 1 day’s work =

1
+
1

=
3
=
1
.

6
12
12
4

So, A and B together can finish the work in 4 days.