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Nine identical machines, each working at the same constant rate, can stitch 27 jerseys in 4 minutes. How many minutes would it take 4 such machines to stitch 60 jerseys?

First, take a deep breath. In this article, you’ll learn a methodical approach that will work on GRE rates problems every single time. On test day, it’ll be tempting to throw away your new habits and go back to old ones. Try to do the opposite. You’ve done all of this studying for a reason!

On problems like this, don’t try anything fancy. A lot of GRE test-takers will try to logically reason their way through this problem, saying something like “well, if 9 machines stitch 27 jerseys in 4 minutes, then 3 machines stitch 9 jerseys in 12 minutes…” That approach is valid but dangerous. Whenever you choose not to write something down, you’re taking away your ability to check your work for mistakes. (By the way, where’s the mistake in the logic described above?)

To start the problem, make a table. Your scratch paper should look like this: Read more