A Pharmacy 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 8 hrs and a machine of type S does the same job in 4 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?
Select the correct option: A) 3 B) 4 C) 2 D) 9 E) 12
Rate of machine R =1/8   Rate of machine S =1/4   since same no of machines used for R and S to do the same work in 2 hrs   So collective rate needed to finish the work in 2 hrs= 1/2   Let the no of machine be x   So, x/8 +x/4 =1/2   3x/8=1/2   x=8/6=1.3=2   So no of machine R is 2   Answer 2
<result>C</result>
A Pharmacy 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 8 hrs and a machine of type S does the same job in 4 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?