Statistics is the study of collecting, organizing, and interpreting data. The three most common measures of central tendency are mean, median, and mode.

The mean (average) is found by adding all values and dividing by how many there are. The median is the middle value when data is sorted — if there is an even number of values, average the two middle ones. The mode is the most frequent value.

Probability measures how likely something is to happen. P(event) = favorable outcomes / total outcomes. A probability of 0 means impossible, 1 means certain. The probability of flipping heads on a fair coin is 1/2 = 0.5 = 50%.