Answer with 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 = 1/6 ; (2 times of B's work)

(A + B)'s 1 day's work = (1/6 + 1/12) = 3/12 = 1/4 .

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

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