9
Adding and subtracting numbers
Textbook: Part 1, lesson 9, pp. 20–21
GoalReview adding and subtracting with place-value units (graphic models).
New words
graphic model · grafik modelten · o‘nlikone · birlikcamel · tuya
Explanation
We add or subtract tens with tens and ones with ones. 24 + 14: 2 tens 4 ones + 1 ten 4 ones = 3 tens 8 ones = 38. In a graphic model a ten can be a stick and a one a dot.
Worked examples
76 − 15: 7 tens 6 ones − 1 ten 5 ones = 6 tens 1 one = 61.
37 + 12: 3 + 1 = 4 tens, 7 + 2 = 9 ones, answer 49.
Class activity
“Place houses”: draw two “houses”: “Tens” and “Ones”. Children lay out a sum with sticks and counters and calculate in both houses.
Practice
1
37 + 12 = ?
49
2
76 − 15 = ?
61
3
Brown wool is 25 kg and white wool is 11 kg. How many kg more brown than white?
14
4
45 l of milk came from one herd and 12 l less from another. How many litres in all?
78