3
Counting brothers and sisters
Discover Mathematics P2: Term 1, Lessons 2–10
GoalCount a class survey, sort the numbers from least to greatest and add them.
New words
survey · asking many people the same questionsibling · a brother or a sisterleast to greatest · from the smallest number to the biggest
Explanation
Let us ask a question: Do you have brothers or sisters? Each child belongs to one group only: no brothers or sisters, only sisters, only brothers, or both. The bars show how many children are in each group. When we add all the bars we get the number of children who answered. To list the numbers from least to greatest, start with the shortest bar and end with the tallest.
Worked examples
In Salma’s class 2 children have no brothers or sisters, 4 have only sisters, 3 have only brothers and 5 have both.
| Group | Children |
|---|---|
| None | 2 |
| Only brothers | 3 |
| Only sisters | 4 |
| Both | 5 |
How many children answered? Add: 2 + 4 + 3 + 5. First 2 + 3 = 5 and 4 + 5 = 9, then 5 + 9 = 14. 14 children answered.
Class activity
Do a family survey. Ask 10 relatives or neighbours: Do you have brothers, sisters, both or none? Write a tally for each group, then write the four numbers from least to greatest.
Practice
1
Mariam’s group has 6 children with sisters and 3 children with brothers. How many more have sisters?
3 (6 − 3 = 3)
2
Write these numbers from least to greatest: 4, 1, 5, 2.
1, 2, 4, 5
3
The bars are 3, 2, 5 and 1 squares tall. How many children are there in all?
11 (3 + 2 + 5 + 1 = 11)
4
Omar says his group is the tallest bar, with 5 children. Is it also the greatest number in the list 3, 2, 5, 1?
Yes. 5 is the greatest number.
5
Nour is in the “both” group. Can she also be in the “only sisters” group?
No. Each child is in only one group.