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 hrs 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 6 hours, how many machines of type R were used?	Choose the correct choice from the following
A) 2 B) 4 C) 6 D) 9 E) 12
Rate of machine R =1/36   Rate of machine S =1/18   since same no of machines used for R and S to do the same work in 6 hrs   So collective rate needed to finish the work in 6 hrs= 1/6   Let the no of machine be x   So, x/36 +x/18 =1/6   x3/36=1/6   x=2   So no of machine R is 2   2nswer 2
<result>A</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 36 hrs 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 6 hours, how many machines of type R were used?