Question 1087139

An old machine requires 3 times as many hours to complete a job as a new machine. When both machine work together, they require 9 hours to complete a job. How many hours would it take then new machine to finish job alone?
<pre>Let time new machine takes be N
Then old machine can do work in 3N hours
Also, new and old machines can do {{{1/N}}} and {{{1/(3N)}}} of work, in 1 hour, respectively
We then get: {{{1/N + 1/(3N) = 1/9}}}
9 + 3 = N ------ Multiplying by LCD, 9N
N, or time new machine takes = {{{highlight_green(matrix(1,2, 12, hours))}}}
That's all! It's as SIMPLE as that!