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How addition and subtraction are linked
Textbook Part 1, pp. 76–77
GoalUnderstand that subtraction is the inverse of addition; write 4 number sentences for one picture.
New words
inverse operation · teskari amalfact family · oila (sonlar oilasi)checking · tekshirish
Explanation
Subtraction is the inverse (opposite) of addition. The numbers 3, 5, 8 form a “fact family”: 3 + 5 = 8, 5 + 3 = 8, 8 − 3 = 5, 8 − 5 = 3. We can check a subtraction with an addition: 8 − 3 = 5, because 5 + 3 = 8.
Worked examples
A seller put out 10 shirts and 2 were left in the evening. Sold: 10 − 2 = 8. Check: 8 + 2 = 10 ✓.
🔵🔵🔵🔵 🔴🔴 → 4 + 2 = 6, 2 + 4 = 6, 6 − 2 = 4, 6 − 4 = 2.
Class activity
Each pair gets three number cards (e.g. 2, 7, 9) and writes the 4 facts in that family.
Practice
1
Write the 4 facts for the family 4, 6, 10.
4 + 6 = 10, 6 + 4 = 10, 10 − 4 = 6, 10 − 6 = 4
2
Check with addition: 9 − 4 = 5
5 + 4 = 9 ✓
3
? − 2 = 6
8
4
Bobur solved 3 problems for the classmate on his left, 2 for the one on his right, and 1 each for the ones in front and behind. How many in all?
7