A company has two types of machines, type R and type S. Operating as a constant rate, a machine R does a certain job in 36 hours and a machine of type S does the same job in 18 hours. If the company used the same number of machines to do the job in 2 hours, how many machines of type R were used?
A. 3
B. 4
C. 6
D. 9
E. 12





In one hr, part of the job done by each machines.....
R - 1/36 , S- 1/18....
Together ..1/12
i.e. If 1 (R + S ) work together it will take 12 hrs...
Hence 6 (R + S) when they work together, it will take 2 hrs...
Ans : C.