56
Subtracting in parts
Textbook Part 2, pp. 32–33
GoalSubtract across ten by splitting the number taken away (15 − 7 = 15 − 5 − 2).
New words
subtracting in parts · bo‘laklab ayirishfirst down to 10 · avval 10 gachapuddle · ko‘lmak
Explanation
When the number taken away is bigger than the ones: 1) split it into two parts — the first part equals the ones; 2) subtract the first part to get down to 10; 3) subtract the rest from 10. 15 − 7 = 15 − 5 − 2 = 10 − 2 = 8.
Worked examples
There were 15 puddles; 5 dried up and then 4 more: 15 − 9 = 15 − 5 − 4 = 6.
On 19 December the night lasted 15 hours and the day 9: 15 − 9 = 6 hours longer.
Class activity
With ten frames: 13 counters (a full frame + 3). Take away 5: first the 3 outside, then 2 from the frame. 8 are left.
Practice
1
14 − 6 = ?
8
2
12 − 5 = ?
7
3
16 − 8 = ?
8
4
Of 18 ice-cream portions, 9 are cherry and the rest peach. How many are peach?
9