1.  A machine P can print one lakh books in 8 hours, machine Q can print the same number of books in 10 hours while machine R can print them in 12 hours. All the machines are started at 9 A.M. while machine P is closed at 11 A.M. and the remaining two machines complete work. Approximately at what time will the work (to print one lakh books) be finished ?
A. 11:30 A.M.
B. 12 noon
C. 12:30 P.M.
D. 1:00 P.M.

Answer: Option D

Explanation:

(P + Q + R)'s 1 hour's work

= ( 1 + 1 + 1 ) = 37 .
8 10 12 120

Work done by P, Q and R in 2 hours

= ( 37 x 2 ) = 37 .
120 60

Remaining work = ( 1 - 37 ) = 23 .
60 60

(Q + R)'s 1 hour's work = ( 1 + 1 ) = 11 .
10 12 60

Now, 11 work is done by Q and R in 1 hour.
60

So,

23 work will be done by Q and R in ( 60 x 23 ) = 23 hours
60 11 60 11

= 2 hours.

So, the work will be finished approximately 2 hours after 11 A.M., i.e., around 1 P.M.