Question 906942

One clerk can file 12 folders per minute and a second clerk, 9. How long will it take them working together to file 672 folders?
<pre>
Both file 9 + 12, or 21 folders in 1 minute
Then, with T being time taken, by both, to file 672, we form a proportion to get:
{{{21/672 = 1/T}}}
21T = 672 ------- Cross-multiplying
T, or time taken = {{{672/21}}}, or {{{highlight_green(32)}}} minutes