A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 20 hrs and a machine of type S does the same job in 60 hours. If the company used the same number of each type of machine to do the job in 3 hours, how many machines of type R were used?	Options:	A) 3	B) 4	C) 5	D) 6	E) 8
Type R completes 1/20 of the job each hour.   Type S completes 1/60 of the job each hour.   Together R and S complete 1/20 +1/60 = 1/15 of the job each hour.   Let n be the number of each type of machine.   3*n*(1/15) = 1 job completed   n = 5   The answer is 5.
<result>C</result>
A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 20 hrs and a machine of type S does the same job in 60 hours. If the company used the same number of each type of machine to do the job in 3 hours, how many machines of type R were used?