Correct Answer: Option D
(P + Q + R)'s 1 hour's work = (1/8 + 1/10 +1/12) = 37/120
Work done by P, Q and R in 2 hours = (37/120 ×2) = 37/60.
Remaining work = (1 – 37/60) = 23/60
(Q + R)'s 1 hour's work = (1/10 + 1/12) = 11/60.
Now, 11/60 work is done by Q and R in 1 hour.
So, 23/60 work will be done by Q and R in (60/11 × 23/60)
=23/11 hours ≈ 2 hours.
So, the work will be finished approximately 2 hours after 11 A.M.,
i.e., around 1 P.M.
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