Three of the most important statistical measures on the GMAT are the mean (or average), median and standard deviation. Familiarize yourself with these terms and these questions will become much easier.

The Mean
To calculate the mean you sum the values in a data set and divide by the number of values. For example, consider the data set 4, 5 and 9. The sum is 18. The number of values in the set is 3. Therefore, the mean is 18 / 3 = 6.

The Median
The median is the middle number in a data set. Consider the following data set: 4, 2, 7, 5, and 1. You determine the median as follows:

* Order the numbers from the smallest number to the largest number.
* 1, 2, 4, 5, and 7.
* The median is therefore 4.

What happens when the number of values in the set is even? For example, 4, 2, 7 and 5.

* Order the numbers.
* 2, 4, 5 and 7.
* Sum the two middle numbers. 4 + 5 = 9.
* Divide by 2. 9 / 2 = 4.5.
* The median is 4.5.

The Standard Deviation
The standard deviation is a measure of how far the values in a data set are from the mean. It can be thought of as the average deviation from the mean.

There is a complicated formula for calculating the standard deviation, but the good news is that we don’t have to use it on the GMAT! However, it is necessary to have a general understanding of what the standard deviation is.

For example, consider the following dataset: 1, 2 and 3. The mean is 2. Now consider a new data set: 0, 2 and 4. The mean is also 2. However, you can see that in the second set the numbers are more widely spread from the mean. Therefore, the second data set has a larger standard deviation.

Questions involving statistical measures are an important part of the GMAT quant section. Be familiar with the meaning of the terms and you will be a long way towards answering these correctly.


_________________