Statistics
Grouped data, histograms and pie charts
Group data into class intervals, read a histogram, and work out the angles in a pie chart.
When there is too much data to list value by value, it gets grouped: 0 to 10, 10 to 20, 20 to 30, and so on. Each group is a class interval, its width is the class size, and how many values land in it is its frequency. Grouping loses the individual numbers and buys you a shape you can actually see.
Bars with no gaps, and slices of a turn
A histogram draws grouped data with its bars touching, because the intervals run on from one another with nothing in between — a gap would mean values that cannot happen. A value sitting exactly on a boundary belongs to the interval it starts: 20 goes in 20-30, not 10-20, so nothing is ever counted twice. A pie chart shows shares of a whole instead: each sector's angle is its share of the total multiplied by 360 degrees, and the angles always add back up to 360.
Have a play
This pie chart shows what a class of 40 children picked for their club. Find out what each slice is and how wide its angle is — nothing here is right or wrong.
Tap any part of the picture.
Worked example
40 people were asked their favourite fruit. 10 said apple. What angle does apple take on a pie chart?
Write the share as a fraction: 10 out of 40, which is 1/4.
The fraction is the whole point of a pie chart. Everything else follows from it.
Try it together
Now let us work out a sector together: 30 children were asked how they travel to school, and 12 of them walk.
Share first, then angle. The same two steps work for every sector of every pie chart.
1.What fraction of the children walk? Write your answer as a fraction.
Have a go
Have a go on your own: in a pie chart of 90 people, 30 chose blue. What angle does that sector take, in degrees? Give just the number.
Hint: Find the fraction who chose it, then take that fraction of a full turn.
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.