The sum of squares of the differences of the average value of each series is divided by the number of items in this series, and then the root sign is opened.

Analysis:

The standard deviation is directly related to denominator (number of items) and score (deviation).

The deviation here is the difference between each number and the average, which is often ignored by GMAT beginners.

Understanding of GMAT mathematical standard variance;

1. The closer the data distribution is to the average, the smaller the standard deviation is; The farther the data distribution is from the average, the greater the standard deviation.

2. The standard deviation is 0, which means that every number in the sequence is equal.

3. Add a constant to each number in the sequence, and the standard deviation remains unchanged.

4. Each number in the sequence is multiplied by a number n that is not 0, and the standard deviation is expanded by n times.