Correct Answer: Option D
A's 1 day's work = 1/15;
B's 1 day's work = 1/20;
(A + B)'s 1 day's work = (1/15) + (1/20) = 7/60
(A + B)'s 4 day's work = ((7/60) x 4) = 7/15.
Therefore, Remaining work = (1 – 7/15) = 8/15
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