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 50 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 5 hours, how many machines of type R were used?
Pick.
A) 18/7  B) 16/7  C) 15/7  D) 22/7  E) 20/7
Rate of machine R =1/50   Rate of machine S =1/20   since same no of machines used for R and S to do the same work in 5 hrs   So collective rate needed to finish the work in 5 hrs= 1/5   Let the no of machine be x   So, x/50 +x/20 =1/5   (2x+5x)/100=1/5   7x=20   x=20/7   So no of machine R is 20/7   Answer 20/7
<result>E</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 50 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 5 hours, how many machines of type R were used?