Need help on a Math Problem..

<p>Problem #1: Mr. Jabos can correct 150 quizzes in 50 minutes. His student aide can correct 150 quizzes in 75 minutes. Working together, how many minutes will it take them to correct 150 quizzes?</p>


<p>Oops that's a familiar math problem,looks like from GMAT rather than from SAT.
Well,Mr J can correct 150 quizzes in 50 mins, so he can correct 150:50 = 3 quizzes in 1 min.
The same as his student who can correct 150 q in 75 m -> 2 q in 1 m
Both of them can correct 3+2=5 q in 1 min if they work together.
So in order to correct 150 q, they must spend 150:5= 30 min if they do together.</p>