(d) 1 p.m
(P + Q + R)’s 1 hours’ work = \(\big(\frac{1}{8}+\frac{1}{10}+\frac{1}{12}\big)\) = \(\frac{37}{120}\)
\(\therefore\) Work done by (P + Q + R) in 2 hours = 2 x \(\frac{37}{120}\) = \(\frac{37}{60}\)
Remaining work = \(\big(1-\frac{37}{60}\big)\) = \(\frac{23}{60}\)
(Q + R)’s 1 hours’ work = \(\big(\frac{1}{10}+\frac{1}{12}\big)\) = \(\frac{11}{60}\)
\(\frac{11}{60}\) of the work is done by (Q + R) in 1 hour
\(\therefore\) \(\frac{23}{60}\) of the work will be done by (Q + R) in \(\frac{23}{60}\) \(\div\)\(\frac{11}{60}\) = 2\(\frac{1}{11}\) hours = 2 hours
So, the work will be finished approximately 2 hours after 11 a.m., i.e., around 1 p.m.