  # Explain Median from a Frequency Table

In this worksheet, students practise finding the median from frequency tables and grouped frequency tables. Key stage:  KS 4

GCSE Subjects:   Maths

GCSE Boards:   AQA, Eduqas, Pearson Edexcel, OCR,

Curriculum topic:   Statistics

Curriculum subtopic:   Statistics Analysing Data

Difficulty level:   #### Worksheet Overview

The definition of median is 'the middle number when the numbers are in order,

This is incredibly easy of the numbers are just a list. All you need to do is order them and cross them off from each end.

It does get a bit harder when they are in a frequency table.

To do this we have to follow three steps.

1) Find the total frequency (this is the same as how many numbers would be there if we wrote it out as a list)

2) Find the position of the middle number

3) Work through the frequencies until we find the position we are looking for.

Example 1: I collect information on shoe sizes and summarise it as shown.

 Shoe Size 3 4 5 6 7 8 9 10 11 12 Frequency 5 7 9 14 21 28 15 6 5 3

Step 1: Find the total frequency.

All we need to do is add up all the frequencies. This gives us 113.

Step 2: Find the position of the median.

To find the position of the median, we add 1 to the total ad half it

(113 + 1) ÷ 2 = 57th

This means the median the 57th number in the list

Step 3: Find the value of the median.

To do this, the easiest way is to find the cumulative frequencies then see where the 57th number lies

 Shoe Size 3 4 5 6 7 8 9 10 11 12 Frequency (Cum 5 12 21 35 56 84 99 105 110 113

We can now see that shoe size 7 starts at the 56th number and ends at the 98th number.

The 57th number must therefore be in the shoe size 7 column.

Example 2: I collect information on the pocket money of 45 students and summarise it in a grouped frequency table.

 Pocket Money (p) 0 ≤ p <10 10 ≤ p <20 20 ≤ p <30 30 ≤ p <40 40 ≤ p <50 40 ≤ p <60 Frequency 4 6 11 10 8 6

a) Find the median group and estimate the median pocket money.

To do these two tasks we start the same way as we did before.

Step 1: Find the total frequency.

All we need to do is add up all the frequencies. This gives us 45.

Step 2: Find the position of the median.

To find the position of the median, we add 1 to the total ad half it

(45 + 1) ÷ 2 = 23

This means the median the 23 rd number in the list

Step 3: Find the value of the median.

To do this, the easiest way is to find the cumulative frequencies then see where the 23rd number lies

 Pocket Money (p) 0 ≤ p <10 10 ≤ p <20 20 ≤ p <30 30 ≤ p <40 40 ≤ p <50 40 ≤ p <60 Frequency 4 6 11 10 8 6 Frequency (cum) 4 10 21 31 39 45

We can now see that 30 ≤ p <40 starts at the 21th number and ends at the 30th number.

The 23rd number must therefore be in the column 30 ≤ p <40 - This is the median group

Estimating the median (Highest level only)

To estimate the median, we need to know where in this group the 23rd lies.

We know the group starts at the 21st position and we are looking for the 23rd, so we need to go 2 positions into this group.

The groups starts at 30 and finishes at 40 so we know it is worth 10.

We can therefore go 2/10 or (1/5th into the group).

As the group is 10 wide, we need to find 1/5 of 10 which is 2.

Adding this onto the start of the group gives an extimated median of 30 + 2 = £32

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