Bar chart (I)
FoundationLong bar = more. Horizontal: categories, vertical: count.
- A bar chart shows amounts by bar length
- Horizontal axis: categories; vertical axis: counts
- Read the scale first: gridlines × scale = value
1Summary 重點摘要
Long bar = more. Horizontal: categories, vertical: count.
2Vocabulary cards Vocabulary
A chart that uses bars of different lengths to show amounts.
A bar in the chart; longer means a bigger amount.
The line lying flat; it shows categories, e.g. fruit names.
The upright line; it shows the counts, e.g. 5, 10, 15.
How much each gridline stands for, e.g. one square = 2.
The collected numbers, e.g. votes for favourite fruit.
The longest bar is the most; the shortest is the least.
Counting with stroke marks, five at a time.
3Step by step Steps
- Part 1: What a bar chart isA bar chart uses bars to show amounts. For example, the class votes for 4 fruits, and each fruit's votes become one bar. The chart shows everything at a glance: the longer the bar, the more people chose that fruit; a shorter bar means fewer people.
- Part 2: The two axesA bar chart has two axes. The horizontal axis lists the categories, such as apple, banana, orange and grape; the vertical axis shows the counts, such as 0, 2, 4, 6, 8. Read both axes first, so you know what the chart is about.
- Part 3: Read the scale firstCheck the scale before reading numbers. If the vertical axis counts by 2 and the orange bar reaches the 3rd gridline, then it is 3 × 2 = 6 oranges. Never assume each square is 1; look at what each square stands for first.
- Part 4: Compare bar lengthsComparing bar lengths answers questions. The apple bar reaches 8 and the banana bar reaches 4: since 8 is bigger than 4, apple is the favourite and banana has fewer; the two fruits differ by 8 − 4 = 4 votes.
- Part 5: Add all the valuesAdding all the bars gives the total. Apple 8, banana 4, orange 6, grape 2: 8 + 4 + 6 + 2 = 20, so the class cast 20 votes in all. This is also a way to check that nothing was left out.
- Part 6: Draw a chart from dataYou can draw a chart from data too. There are 5 cats, 7 dogs and 3 rabbits: draw 3 bars, cat to 5, dog to 7 and rabbit to 3, write the names under the bars, add a title, and the bar chart is complete.
4Diagrams Diagrams
5Worked example Example
Example: a bar chart has a scale of 2 per gridline. The apple bar reaches the 4th gridline and the orange bar the 5th. Which is more, and by how much?
- Read the apple first: 4 gridlines × 2 = 8, so there are 8 apples.
- Read the orange next: 5 gridlines × 2 = 10, so there are 10 oranges.
- Compare the two numbers: 10 is bigger than 8, so orange is more.
- Find the difference: 10 − 8 = 2, so orange has 2 more than apple.
- Answer: Answer: orange is more, by 2. The first step in reading a bar chart is to check the scale: count how many gridlines the bar reaches, then multiply by what each gridline stands for to get the true number.
6Common mistakes Mistakes
7Quick check Quick check
Q1What does a longer bar mean?
Q2What does the horizontal axis usually show?
Q3Scale is 5 per line and the bar reaches the 3rd line. The value is?
Q4Apple 8, banana 4, orange 6. What is the total?
Q5Dog bar reaches 7, rabbit bar 3. How many more dogs?
8Recap Recap
- A bar chart shows amounts by bar length
- Horizontal axis: categories; vertical axis: counts
- Read the scale first: gridlines × scale = value
- Longest bar is the most, shortest is the least
- How many more? Subtract the two values