# Calculating Combinations in Your Head

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.

## 4 comments

kave on August 8th, 2010 at 9:23 pm

this is amazing.. thanks

Srikanth on August 9th, 2010 at 10:32 am

This is Wonderful. Especially useful when value of r is low compared to value of n in n C r.

Maciej on August 10th, 2010 at 11:37 am

thank you for this formula

shibbirahamed on August 31st, 2010 at 6:57 am

wow! its helpful for pacing dude.