(a) 11:30 A.M.
(b) 12 noon
(c) 12:30 P.M.
(d) 1:00 P.M.
Explanation:
(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 x 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 x 23/60) = 23/11 = 2 hours