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 10 hrs and a machine of type S does the same job in 5 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 option:
A) A)3
B) B)4
C) C)6
D) D)9
E) E)12
Rate of machine R =1/10   Rate of machine S =1/5   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/10 +x/5 =1/2   3x/10=1/2   x=30/5= 
<gadget id="calculator">30/5</gadget>
<output>6</output>
6   So no of machine R is 6   Answer 6
<result>C</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 10 hrs and a machine of type S does the same job in 5 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?