arithmetic - a machine a can print one lakh books in 8 hours machine b can print the same number of books in 10 hours while machine c can print them in 12 hours all the machines are started at 9 am while machine a is closed at 11 am and the remaining two - skillgun

Solution: (A+B+C)'s 1 hour's work = (1/8 + 1/10 + 1/12) = 37/120.
work done by A, B and C in 2 hours = (37*2/120) = 37/60.
Remaining work = (1 - 37/60) = 23/60.
(B+C)'s 1 hour's work = (1/10 + 1/12) = 11/60.
Now, 11/60 work is done by B and C in 1 hour.
so, 23/60 work will be done by B and C 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.