Concise Selina Solutions for Class 9 maths Chapter 19 Mean and Median Definition


The mean (average) of a data set is found by adding all numbers in the data set and then dividing by the number of values in the set. The median is the middle value when a data set is ordered from least to greatest. The mode is the number that occurs most often in a data set.

Mean vs Median

The mean (informally, the "average ") is found by adding all of the numbers together and dividing by the number of items in the set: 10 + 10 + 20 + 40 + 70 / 5 = 30. The median is found by ordering the set from lowest to highest and finding the exact middle. The median is just the middle number: 20.

The median is defined as the "middle term" in a set. In the set {0, 3, 5}, the median is 3. If the set has an even number of terms, the median is the average of the middle two terms. Since the numbers are consecutive, the mean and the median are the same.