GRE Math formula sheet : Statistics

Statistics

Average or mean:

For a set of n numbers: total sum / n

Median:

Middlemost value when numbers are arranged in ascending order; for an even amount of numbers, take the average of the middle two

Mode:

The number that occurs most frequently

Example:

2, 3, 3, 4, 5, 6, 6, 6, 7: Mean = 42/9, Median = 5, Mode = 6

If the numbers in a set are evenly spaced, then the mean and median of the set are equal: {30, 35, 40, 45, 50, 55}

Weighted average:

(proportion) x (group A average) + (proportion) x (group B average) + …

Range:

Greatest value – least value

Standard deviation:

If you’re given a set of n numbers a, b, c, … with a mean m:

The standard deviation represents the average distance the data values are away from the mean.

Variance is the value inside the square root of the standard deviation = SD² 

If the standard deviation of a set of numbers is k, then k = 1 unit of standard deviation.