# GMAT® Quant Practice - Counting Methods

Concept: Selecting one or more objects

This GMAT Math practice question is a problem solving question in counting methods. A very interesting question.

1. 5
2. 21
3. 33
4. 60
5. 6

#### Video Explanation

##### List down possibilities: From only 1 box all the way to all 6

If only one of the boxes has a green ball, it can be any of the 6 boxes. So, we have 6 possibilities.
If two of the boxes have green balls and then there are 5 consecutive sets of 2 boxes. 12, 23, 34, 45, 56.
If 3 of the boxes have green balls, there are 4 possibilities: 123, 234, 345, 456.
If 4 boxes have green balls, there are 3 possibilities: 1234, 2345, 3456.
If 5 boxes have green balls, there are 2 possibilities: 12345, 23456.
If all 6 boxes have green balls, there is just 1 possibility.

Total number of possibilities = 6 + 5 + 4 + 3 + 2 + 1 = 21.

Choice B is the correct answer.

### Target Q-51 in GMAT Quant. Make it a reality @ INR 3000!

Most Comprehensive & Affordable GMAT Online Course for Quant. 20 topics.
Focused preparation for the hard-to-crack eggs in the GMAT basket! 