Primary 4 maths · Operations · About 12 minutes
Three groups: set the extra aside
Set aside an extra amount, then use equal parts to find a group
Start the interactive lesson →Practise: Find the number of blue buttons
What you will learn
- Set aside an extra amount, then use equal parts to find a group
Models used: tables, bar models, number sentences, stories.
Before you start
Set the extra aside
There are 92 buttons. Red has 8 more than blue. Blue has 3 times as many as green. Find blue.
The table keeps the three clues together.
The information from this question Clue Information All buttons 92 Red compared with blue 8 more Blue compared with green 3 times as many Set aside the extra 8 red buttons. Red and blue now match.
92 − 8 = 84
The information from this question Clue Information All buttons 92 Red compared with blue 8 more Blue compared with green 3 times as many Green is 1 part. Blue is 3 parts, and the red buttons left are also 3 parts.
1 + 3 + 3 = 7 parts
The information from this question Clue Information All buttons 92 Red compared with blue 8 more Blue compared with green 3 times as many Share the 84 equally among the 7 parts, then use 3 parts for blue.
84 ÷ 7 = 12; 3 × 12 = 36
The information from this question Clue Information All buttons 92 Red compared with blue 8 more Blue compared with green 3 times as many
Worked example: Try one step at a time
There are 79 buttons. Red has 9 more than blue. Blue has twice as many as green. Find blue.
| Clue | Information |
|---|---|
| All buttons | 79 |
| Red compared with blue | 9 more |
| Blue compared with green | 2 times as many |
First set aside the extra red buttons.
The information from this question Clue Information All buttons 79 Red compared with blue 9 more Blue compared with green 2 times as many How many buttons remain?
70
Now count red, blue and green parts.
The information from this question Clue Information All buttons 79 Red compared with blue 9 more Blue compared with green 2 times as many How many equal parts are there?
5
Share the remaining buttons equally among those parts.
The information from this question Clue Information All buttons 79 Red compared with blue 9 more Blue compared with green 2 times as many How many buttons are in one part?
14
Blue has two of those equal parts.
The information from this question Clue Information All buttons 79 Red compared with blue 9 more Blue compared with green 2 times as many How many blue buttons are there?
28
Put the extra back to check all three groups.
14 + 28 + 37 = 79
The information from this question Clue Information All buttons 79 Red compared with blue 9 more Blue compared with green 2 times as many
Common mistakes to discuss
- Leave the extra in the equal parts. Set it aside before dividing the remaining total.
- Count the blue parts only. Include the matching red parts and the green part too.
Check your understanding
- Set aside the extra amount.
- Count equal parts and use one part to find a group.
Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.
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