A works twice as fast as B.If B can complete a work in 18 days independently,the number of days in which A and B can together finish the work is:

4 days
6 days
8 days
10 days

Correct Answer: 6 days

Explanation:

Ratio of rates of working of A and B =2:1. So, ratio of times taken =1:2

Therefore, A's 1 day's work=1/9

B's 1 day's work=1/18

(A+B)'s 1 day's work= 1/9 + 1/18 = 1/6

so, A and B together can finish the work in 6 days

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