You have read picture graphs and bar graphs where each picture or each square stood for 1. When the numbers get big, one picture can stand for several. Your facts of 2, 5 and 10 make these graphs quick to read.
Why it works
Drawing 25 pictures for 25 votes takes a lot of room. If each picture stands for 5 votes, 5 pictures are enough. Reading the graph is then an equal-groups problem: 5 circles, each worth 5, is $5 \times 5 = 25$. Half a picture stands for half as many: with a key of 10, half a picture is 5.
Key idea
Always read the key or the scale first. Multiply the number of symbols by what each one stands for. On a bar graph, check how much each line on the scale is worth.
Worked example: Read a picture graph
In the graph above, how many votes did Blue get? How many more than Green?
- Blue has 5 circles. $5 \times 5 = 25$ votes.
- Green has 2 circles: $2 \times 5 = 10$ votes.
- $25 - 10 = 15$ more.
Answer: 25 votes; 15 more
Worked example: Read a bar graph
How many students chose Dogs?
- Each line on the scale is 2 more.
- The Dogs bar ends halfway between 6 and 8.
- Halfway between 6 and 8 is 7.
Answer: 7 students
Common mistake
Counting each picture as 1. If the key says each circle is 5 votes, 3 circles are 15 votes, not 3. Check the key every time, because different graphs use different keys.