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 36 hours and a machine of type S does the same job in 18 hours. If the company used the same number of each type of machine 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















Rate of Type R * # of Machines + Rate of Type S * # of Machines = Rate Together
let M = # of machines
M/36 + M/18 = 1/2
M = 6
ANSWER: C. 6