So, it's test day, and you find yourself working on a particularly challenging counting question involving combinations.

The last step in the solution requires you to calculate:


Do you evaluate this expression in your head, or do you use the somewhat cumbersome combination formula?

After viewing this video, you should be able to perform most combination calculations in your head.

About Beat The GMAT

Eric Bahn is the Founder of Beat The GMAT, an MBA applicant community serving 1 million+ visitors/year.  In July, Beat The GMAT will be launching a new set of GMAT practice questions called Smart GMAT Practice.