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Maths

Frequency tables: finding averages

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Frequency tables: finding averages

​​In a nutshell

Just like for sets of values, the mean, median, mode and range can be found from frequency tables too. The only difference is that these averages might refer to a category, rather than an individual number.


PROCEDURE

Mean

Create a new column: 'number ×\times frequency' and calculate these values. Next, find the sum of all these values, then divide this number by the total frequency. 

Median

Identify the category containing the middle value: use n+12\frac{n+1}{2} where n is the total frequency to find the middle position.

Mode

Identify the category with the highest frequency.

Range

Calculate the difference between the highest and lowest in the 'number of' column.



Example

This frequency table shows the number of siblings pupils in a class of 2323 have:


Number of siblings

Frequency

00​​

66​​
11​​
1212​​
22​​
33​​
33​​
22​​
44​​
00​​

Find the mean, median, range and mode.


1. Mean: 

Add the third column to the table.

Number of siblings ×\times frequency
0×6=00\times6=0​​​
1×12=121\times12=12​​
2×3=62\times3=6​​
3×2=63\times2=6​​
4×0=04\times0=0​​

Use the formula:

sum of ’number×frequency’ columntotal frequency=12+6+66+12+3+2=2423=1.043 (to 3 d.p)\frac{\text{sum of 'number}\times \text{frequency' column}}{\text{total frequency}}=\frac{12+6+6}{6+12+3+2}=\frac{24}{23}=\underline{1.043} \text{ (to 3 d.p})​​


Note: The total number of students was given in the question here, but often you will need to calculate it yourself.


2. Median:  

Identify the middle position.

(n+1)2=(23+1)2=12\frac{(n+1)}{2}=\frac{(23+1)}{2}=12​​

The median is the category containing the 12th12th value cumulatively: 1\underline1


3. Mode: 

Identify the category with the highest frequency.

1\underline1


4. Range: 

Work out the difference between the highest and lowest number of siblings.

30=33-0 = \underline3​​


Note: 44 is not used here as there is no one with 44 siblings.​




Want to find out more? Check out these other lessons!

Averages from frequency tables

Frequently Asked Questions (FAQ)

FAQs

  • Question: How do I find the range from a frequency table?

    Answer: To find the range from a frequency table, find the difference between the highest and lowest in the 'number of' column.

  • Question: How do I find the mode from a frequency table?

    Answer: The mode in a frequency table is the value of the category with the highest frequency.

  • Question: How do I find the median from a frequency table?

    Answer: To find the mean from a frequency table, find the category containing the middle value: use (n+1)÷2 where n is the total frequency to find the middle position.​

  • Question: How do I find the mean from a frequency table?

    Answer: To find the mean from a frequency table: Create a new column: 'number × frequency' and calculate these values. Next, find the sum of all these values, then divide this number by the total frequency.

Theory

Exercises

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