Bunuel wrote:
A works twice as fast as B. If B can complete a piece of work independently in 12 days, then the number of days taken by A and B together to finish the work is:
A. 4
B. 6
C. 8
D. 9
E. 10
We can see that the rate of B = 1/12, and hence the rate of A = 2 x 1/12 = 1/6. Thus, their combined rate is:
1/6 + 1/12 = 2/12 + 1/12 = 3/12 = 1/4.
So it will take 4 days to complete the job when working together.
Answer: A
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