Problem Solving

robvspencer wrote:Can someone explain the mathematical jargon of 9C3 and how it is calculated please. Not sure how everyone is getting 84 from that and feeling inferior due to it -_-

We use the notation nCr to count the number of ways to select r things from a group of n things when the order of the selected objects does not matter.

For example, if you have 7 friends, and you want to select 3 of them to attend your party, this can be accomplished in 7C3 ways.
If you have 10 employees and you want to select 4 of them to be on a committee, this can be accomplished in 10C4 ways.

The formula is: nCr = n!/(r!)(n-r)!
So, 9C3 = 9!/(3!)(9-3)! = 9!/(3!)(6!) = 84

If you're interested, we have a free video on calculating combinations in your head: https://www.gmatprepnow.com/module/gmat-counting?id=789

Cheers,
Brent