1.  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 :
A. 4 days
B. 6 days
C. 8 days
D. 18 days

Answer: Option A

Explanation:

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

Therefore 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.