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Time and Work - General Aptitude

Q1:

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.

ANS:D - 1:00 P.M.

(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 = 2 hours.
60 11 60 11
So, the work will be finished approximately 2 hours after 11 A.M., i.e., around 1 P.M.