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 40 hrs and a machine of type S does the same job in 20 hours. If the company used the same number of each type of machine to do the job in 4 hours, how many machines of type R were used?  Choose the correct choice from the following options:
A) 11/3  B) 10/3  C) 8/3  D) 13/3  E) 7/3
Rate of machine R =1/40   Rate of machine S =1/20   since same no of machines used for R and S to do the same work in 4 hrs   So collective rate needed to finish the work in 4 hrs= 1/4   Let the no of machine be x   So, x/40 +x/20 =1/4   3x/40=1/4   x=10/3   So no of machine R is 10/3   Answer 10/3
<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 40 hrs and a machine of type S does the same job in 20 hours. If the company used the same number of each type of machine to do the job in 4 hours, how many machines of type R were used?