Discover Mathematics P4: Term 2, Unit 11, Lessons 1–5
GoalRead single and double bar graphs, use a scale, and choose which graph fits the data.
New words
bar graph · a graph that uses bars; the length of a bar shows how manydouble bar graph · a bar graph with two bars for each category, in two colours, to compare two sets of datascale · what one block or one step of the graph stands forkey · a note that tells what each colour means
Explanation
A bar graph shows how many items are in each category. The longer the bar, the more items. A single bar graph shows one set of data, such as the favourite fruit of one class. A double bar graph shows two sets of data side by side, with two colours and a key, so that we can compare them, for example boys and girls. Before you read a graph, read the title, the names of the categories, the key and the scale. When the numbers are big, one block can stand for more than one item, for example 1 block = 10 books. To find a total, add the bars. To find how many more, subtract the shorter bar from the longer bar.
Worked examples
Class 4B voted for its favourite fruit. The bars show oranges 12, bananas 9, guavas 6 and dates 3. How many children voted? Add the bars: 12 + 9 + 6 + 3 = 30 children. How many more chose oranges than dates? Subtract: 12 − 3 = 9 more.
A double bar graph compares boys and girls. The first bar of each pair is for boys and the second is for girls. Football: boys 14, girls 6. Skipping rope: boys 3, girls 11. How many more boys than girls chose football? 14 − 6 = 8. How many children chose skipping rope? 3 + 11 = 14.
A library counts the books borrowed each day. Each block stands for 10 books. Sunday has 7 blocks, so 7 × 10 = 70 books. Monday has 2 blocks: 2 × 10 = 20 books. Sunday had 70 − 20 = 50 more books than Monday. Always multiply the number of blocks by the scale.
Class activity
Our class graph. Ask 15 family members or friends which drink they like best: tea, juice or water. Make a tally, then draw a bar graph on squared paper with one square for each person. Write two questions about your graph and ask a friend to answer them.
Practice
1
The graph shows the pets of Class 4C. Which pet is the most common, and how many more children have it than birds?
Fish, 10 children. 10 − 5 = 5 more than birds.
2
How many pets are there in all in the graph of Class 4C?
10 + 8 + 5 + 2 = 25 pets.
3
The double bar graph shows pages read by two classes. On which day did both classes read the same, and how many pages did they read together on Tuesday?
Wednesday, when both bars have 7. On Tuesday 8 + 5 = 13 pages.
4
Which graph is better to compare how many boys and how many girls like each sport: a single or a double bar graph?
A double bar graph, with one colour for boys and another for girls.
5
In Mina’s graph each block stands for 5 stickers. The bar for Friday is 6 blocks long. How many stickers is that?
