A **central tendency** is a single value or average that represents the whole set of data. It is referred to as the central location of data distribution. The value that is represented as a central tendency is within the range of the data. There are 3 measures of central tendency. They are:

**Mean (x̅ or μ)****Median(M)****Mode(Z)**

**Mean**

Mean is the sum of all the values in the data set divided by the number of values in the data set. It is also called the Arithmetic Average. If x_{1, }x_{2,} x_{3},……, x_{n} are the values of a data set then the mean is denoted as x̅ (x bar) and the formula is calculated as:

### x̅ = (x_{1 }+ x_{2} + x_{3 }+ …… + x_{n}) / n

**Example:**

The mean of the data 10, 30, 40, 20, 50 is

Mean = (sum of all data values) / (number of values)

Mean = (10 + 30 + 40 + 20+ 50) / 5=30

**Median**

A Median is a middle value for a sorted data. The sorting of the data can be done either in ascending order or in descending order. A median divides the data into two halves. The formula for median:

If the number of values (n value) in the data set is odd then the formula to calculate median is:

### Median = ((n + 1)/2)^{th} term

If the number of values (n value) in the data set is even then the formula to calculate median is:

### Median = [(n/2)^{th} term + {(n/2) + 1}^{th }term] / 2

**Example 1:**

The median of the data 30, 40, 10, 20, 50 is:

Step 1:Order the given data in ascending order as:10, 20, 30, 40, 50

Step 2:Check n (number of terms of data set) is even or odd and find the median of the data with respective ‘n’ value.

Step 3:Here, n = 5 (odd) then Median = [(n + 1)/2]^{th}term 10, 20, 30, 40, 50The median of the data is [(5 + 1)/2]

^{th}term is 30.

**Example 2:**

25, 12, 5, 24, 15, 22, 23, 25

Step 1:Order the given data in ascending order as:5, 12, 15, 22, 23, 24, 25, 25

Step 2:Check n (number of terms of data set) is even or odd and find the median of the data with respective ‘n’ value.

Step 3:Here, n = 8 (even) then,Median = [(n/2)

^{th}term + {(n/2) + 1)^{th}term] / 2Median = [(8/2)

^{th}term + {(8/2) + 1}^{th}term] / 2 = (22+23) / 2 = 22.5

**Mode**

A mode is the most frequent value or item of the data set. A data set can generally have one or more than one mode value. If the data set has one mode then it is called “Uni-modal”. Similarly, If the data set contains 2 modes then it is called “Bimodal” and if the data set contains 3 modes then it is known as “Trimodal”. If the data set consists of more than one mode then it is known as “multi-modal”(can be bimodal or trimodal). There is no mode for a data set if every number appears only once.

**Example 1:**

If the data set is {1, 2, 2, 3, 3, 4, 5} then it has 2 modes i.e, 2 and 3 (bi-modal). Since, both the values 2 and 3 are repeating twice in the data set.

**Example 2:**

If the data set is {15, 42, 65, 65, 95} then the mode is 65 (uni-modal). Since 65 is the only repeating value in the data set.

**Range**

It is the difference between the highest value and the lowest value. It is a way to understand how the numbers are spread in a data set. Formula to find Range is:

### Range = Highest value – Lowest Value

**Example:**

If the data set is {12, 19, 6, 2, 15, 4} then the lowest value is 2 and the highest value is 19.

So the range is 19 − 2 = 17.

**Reading Bar Charts: Putting it Together with Central Tendency**

**Question 1. Finding Mean for the above bar chart.**

Mean = (sum of all data values) / (number of values)

Mean = (5 + 7 + 9 + 6) / 4 = 27 / 2 = 6.75

**Question 2. Finding the Median for the above bar chart:**

Order the given data in ascending order as: 5, 6, 7, 9

Here, n = 4 (number of students which is even)

Median = [(n/2)

^{th}term + {(n/2) + 1}^{th}term] / 2Median = (6 + 7) / 2 = 6.5

**Question 3. Finding Mode for the above bar chart:**

Mode = most frequent value = 9 (highest value)

**Question 4. Finding the range for the above bar chart:**

Range = highest value – lowest value

Range = 9 – 5 = 4