Question

11. An old machine requires three times as many hours to complete a job as

a new machine. When both machines work together, they require 9 hours
to complete a job. How many hours would it take the new machine to
finish the job operating alone?

Answer 1

Explanation:

`9(r_n+r_o)=1\\ \\ r_n+r_o=(1)/(9)\\ \\ r_o=(r_n)/(3)\\ \\ r_n+(r_n)/(3)=(1)/(9)\\ \\ (4r)/(3)=(1)/(9)\\ \\ 4r=(1)/(3)\\ \\ r=(1)/(12)\\ \\ \text{So working alone it would take the new machine 12 hours to finish the job.}`