1
Building a bar graph
Discover Mathematics P2: Term 2, Lessons 111–120
GoalBuild a bar graph from tally marks: count, write totals, and draw bars of the right height.
New words
tally marks · lines we draw to count; every fifth line crosses fourdata · the facts we collect, such as votestitle · the name of the graphtotal · all the votes in one row
Explanation
Here is how to build a bar graph. First collect the data and make tally marks, one mark for each child. Every fifth mark crosses the other four. Second, count the tally marks in each row and write the total. Third, draw one bar for each row, as tall as its total, all with the same width. Last, write a title. In our class vote, football got 7, hide and seek 5, skipping rope 4 and marbles 3.
Worked examples
The tally chart shows the votes. Football has one group of five and 2 more: 7. Adding all the totals: 7 + 5 + 4 + 3 = 19 children voted.
The same data as a bar graph. Each bar is as tall as the total: football 7, hide and seek 5, skipping rope 4, marbles 3.
Check your graph. The tallest bar is football, so football is the favourite game. The shortest bar is marbles. 7 − 3 = 4 more children chose football than marbles.
Class activity
Class vote at home. Ask family and neighbours which drink they like best: juice, milk or water. Make tally marks on a paper. Count them, write the totals and draw a bar for each drink. Give your graph a title. Which bar is the tallest?
Practice
1
How many children voted in all?
6 + 4 + 3 = 13 children.
2
Which bar would be the tallest for this tally?
Juice, because it has the most tally marks (6).
3
How tall is the marbles bar?
The marbles bar is 3 tall.
4
Mina asks 10 children. Football got 4, swimming 3, tennis 2. How many children chose karate?
4 + 3 + 2 = 9, so 10 − 9 = 1 child chose karate.
5
Write a good title for the graph about favourite games.
For example “Our favourite games”.