Correct Answer: Option B
Work done by X in 4 days = (1/20 x 4) = 1/5.
Remaining work =(1 – 1/5) = 4/5.
(X + Y)'s 1 day's work = (1/20 + 1/12)
= 8/60 = 2/15.
Now, 2/15 work is done by X and Y in 1 day.
So, 4/5 work will be done by X and Y in (15/15 x 4/5)= 6 days
Hence, total time taken = (6 + 4) days = 10 days.
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