2
Equal groups in the market
Discover Mathematics P3: Term 1, Lessons 11–20
GoalFind the total of equal groups with repeated addition and skip counting.
New words
equal groups · groups that have the same number of thingsrepeated addition · adding the same number again and againskip counting · counting forward in jumps of the same sizetotal · how many there are in all
Explanation
In a market things are often sold in equal groups, such as 5 bags with 4 oranges in each bag. To find the total, add the same number again and again: 4 + 4 + 4 + 4 + 4 = 20. This is repeated addition. You can also skip count: 4, 8, 12, 16, 20. There are 20 oranges. Equal groups have the same number in every group. If the groups are different sizes, such as 4, 3 and 5, they are not equal groups, so we cannot skip count by one number. Always check each group first.
Worked examples
A seller has 6 trays with 2 eggs in each tray. Add: 2 + 2 + 2 + 2 + 2 + 2 = 12. Skip counting gives 2, 4, 6, 8, 10, 12. There are 12 eggs.
Farida buys 3 bunches with 5 bananas in each bunch. Skip count by 5: 5, 10, 15. She has 15 bananas. As an addition: 5 + 5 + 5 = 15.
These are not equal groups. The three bunches of carrots have 4, 3 and 5 carrots. We cannot skip count, but we can still add: 4 + 3 + 5 = 12 carrots.
Class activity
Market game. Take 20 beans or pebbles. Make equal groups of 2, then of 4, then of 5. For each, say how many groups you made and write a repeated addition, such as 5 + 5 + 5 + 5 = 20. Then try groups of 3. What happens?
Practice
1
There are 4 baskets with 3 tomatoes in each. How many tomatoes are there in all?
3 + 3 + 3 + 3 = 12 tomatoes.
2
Write a repeated addition for 6 bags with 5 sweets in each bag. What is the total?
5 + 5 + 5 + 5 + 5 + 5 = 30 sweets.
3
A seller puts 7 apples in each of 3 boxes. Skip count to find how many apples.
7, 14, 21. There are 21 apples.
4
Are these equal groups? Explain.
No. The groups have 4, 4 and 3 oranges, so they are not the same size.
5
Hana says 8 + 8 + 8 + 8 gives the same total as counting 8, 16, 24, 32. Is she right? What is the total?
Yes. Both give 32.