69
Addition and subtraction as inverses
Textbook Part 2, pp. 58–59
GoalCheck subtraction with addition for two-digit numbers too; fact families.
New words
inverse operations · teskari amallarvowel · unli harfconsonant · undosh harf
Explanation
Addition and subtraction undo each other. If 23 + 6 = 29, then 29 − 6 = 23 and 29 − 23 = 6. To check a subtraction, add the difference and the number taken away: you should get the starting number.
Worked examples
According to the textbook the Uzbek alphabet has 29 letters, 6 of them vowels: 29 − 6 = 23 consonants. Check: 23 + 6 = 29 ✓.
The little bun rolled 20 m, then another 30 m: 20 + 30 = 50 m.
Class activity
Pairs: one solves a subtraction, the other checks it with addition. Then they swap roles.
Practice
1
Check with addition: 58 − 26 = 32
32 + 26 = 58 ✓
2
Write the 4 facts for the family 41, 35, 76.
41 + 35 = 76, 35 + 41 = 76, 76 − 35 = 41, 76 − 41 = 35
3
_ + 24 = 69
45
4
A shape is not a triangle or a hexagon; it has fewer than 5 corners. What could it be?
A quadrilateral (square or rectangle)