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 24 hrs and a machine of type S does the same job in 12 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?
Choose the correct choice from the following.
A) 3 B) 4 C) 6 D) 8 E) 12
Type R completes 1/24 of the job each hour.   Type S completes 1/12 of the job each hour.   Together R and S complete 1/24 +1/12 = 1/8 of the job each hour.   Let n be the number of each type of machine.   2*n*(1/8) = 1 job completed   n = 4   The answer is 4.
<result>B</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 24 hrs and a machine of type S does the same job in 12 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?