Answer: C. 6
Step-by-step explanation:
Given : Time taken by Machine R to do the job = 36 hours
Time taken by Machine S to do the job = 18 hours
Let x be the number of each type of machine to do the job.
Then , according to the question the required equation will be :-
[tex]\dfrac{x}{36}+\dfrac{x}{18}=\dfrac{1}{2}\\\\\Rightarrow\ x(\dfrac{1}{36}+\dfrac{1}{18})=\dfrac{1}{2}\\\\\Rightarrow\ \dfrac{x}{12}=\dfrac{1}{2}\\\\\Rightarrow\ x=\dfrac{12}{2}=6[/tex]
Hence, the number of machines of type R were used =6
