Week 7 · Clocks in five-minute steps and division · 3 lessons
3
Making equal groups
Discover Mathematics P3: Term 1, Lessons 21–30
GoalPut things into equal groups of a given size, find how many groups there are, and tell sharing from grouping.
New words
grouping · putting things into groups of the same sizegroup size · how many are in each groupnumber of groups · how many groups we make
Explanation
Sometimes we know how many are in each group, and we want to know how many groups there are. There are 18 oranges and each bag holds 3. How many bags do we need? Make groups of 3 until all the oranges are used: 3, 6, 9, 12, 15, 18. That is 6 groups, so 18 ÷ 3 = 6. In sharing, we know the number of groups and find how many are in each. In grouping, we know the size of each group and find the number of groups. Both are division, and both use the same multiplication fact: 3 × 6 = 18. On a number line we count the jumps of 3 from 0 to 18.
Worked examples
Twenty eggs are packed in trays that hold 5 eggs each. Make groups of 5: 5, 10, 15, 20. That is 4 trays, so 20 ÷ 5 = 4.
Twelve children make teams of 4. The tape shows 3 teams. 12 ÷ 4 = 3, so there are 3 teams.
Sharing: 12 flowers shared among 3 vases gives 4 flowers in each vase. Grouping: 12 flowers put in vases of 3 flowers each gives 4 vases. The question is different, but both are 12 ÷ 3 = 4.
Class activity
Group hunt. Take 30 beans or pasta shells. Make groups of 5, then groups of 6, then groups of 10. For each, write the group size, the number of groups and the division. Then try groups of 4. What happens to the beans that are left?
Practice
1
A bag holds 4 oranges. How many bags are needed for 24 oranges?
24 ÷ 4 = 6 bags.
2
Is it sharing or grouping? (a) 20 pencils are shared among 4 children. (b) 20 pencils are put into boxes of 4.
(a) is sharing: 5 pencils each. (b) is grouping: 5 boxes.
3
How many jumps of 4 are there from 0 to 24? Write the division.
6 jumps. 24 ÷ 4 = 6.
4
Write a division story for 15 ÷ 5 = 3.
For example: 15 stickers are put on pages with 5 stickers on each page. That makes 3 pages.
5
A boat carries 6 children at a time. How many trips are needed for 30 children?
