Mode, median and range · Usually met around P5
Grouped frequency
Each value in one group: 129 in 120–129, 130 in the next.
How to do it
Method
Each value in one group: 129 in 120–129, 130 in the next
125, 131, 138, 122 → 120–129: 2, 130–139: 2
Another way
Add up to check
2 + 2 = 4 values
In full
When there are many different values (heights, say), group them first: 10 values a group, 120–129, 130–139… Each piece of data goes in exactly one group: 129 in 120–129, 130 in the next. Tally the data one by one to count each group (its frequency), make a frequency table, then draw a frequency diagram: a bar a group, with no gaps between bars because the data run on. Read a bar against the scale at its top. Once grouped, you know how many are in each group, not each exact value. Check: the frequencies add up to how many data there are.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
Data: 36, 34, 28, 15, 23, 18, 15, 39, 43, 36. Grouped in tens, how many values are in the group 10–19?
Show the answer and working
Answer: 3
Go through them one by one: 3 values lie from 10 to 19, both included.
Example 2
The frequency diagram shows some children's heights (cm). How many are 110–119 cm tall?
Show the answer and working
Answer: 8
Read the 110–119 bar: its top is level with 8, so 8 children.
Example 3
Grouping in tens, 39 belongs in the group 40–49.
True or false?
Show the answer and working
Answer: False
The group 40–49 runs from 40 to 49, both included; anything below 40 or above 49 is in another group.
Practise it in the game →Mode, median and range · Free to start, unlimited questions, no download