Math 1A Singapore-Addition and Subtraction-Chapter 6.2
Addition and Subtraction
How many balls
are there altogether?
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à
Make 10 first and count extra balls.
⚽.⚽.⚽.⚽.⚽
⚽.⚽.⚽.⚽.⚽
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⚽.⚽.⚽
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10 + 3 = 13.
So, there are 13 balls altogether.
Now,
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à
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Here,
9 + 4
= 9 + 1 + 3
= 10 + 3
= 13
1. Add by making 10 first.
(a) 5 + 9 = 🟦.
Solution:
5 + 9
= 4 + 1 + 9
= 4 + 10
= 14
So, 5 + 9 = 14.
(b) 7 + 8 = 🟦.
Solution:
7 + 8
= 5 + 2 + 8
= 5 + 10
= 15
So, 7 + 8 = 15.
2. Complete the
addition sentences.
(a) 9 + 1 = 🟦. 9 + 8 = 🟦.
(b) 8 + 2 = 🟦. 8
+ 6 = 🟦.
(c) 1 + 9 = 🟦. 3
+ 9 = 🟦.
(d) 2 + 8 = 🟦. 5
+ 8 = 🟦.
(e) 3 + 7 = 🟦. 6
+ 7 = 🟦.
Solution:
(a) 9 + 1 = 10. 9 + 8 = 17.
(b) 8 + 2 = 10. 8 + 6 =
14.
(c) 1 + 9 = 10. 3 + 9 =
12.
(d) 2 + 8 = 10. 5 + 8 =
13.
(e) 3 + 7 = 10. 6 + 7 =
13.
3. Add 13 and 4.
Solution:
13 + 4
= 10 + 3 + 4
= 10 + 7
= 17
So, 13 + 4 = 17.
4. Complete the
addition sentences.
(a) 5 + 4 = 9. (b) 2 + 8 = 10.
15 + 4 = 🟦.
12 + 8 = 🟦.
5 + 14 = 🟦. 2 + 18 = 🟦.
Solution:
(a) 5 + 4 = 9. (b) 2
+ 8 = 10.
15 + 4 = 19. 12 + 8 = 20.
5 + 14 = 19. 2 + 18 = 20.
5. Subtract 4
from 16.
Solution:
16 – 4
= 10 + 6 – 4 [subtract
4 from 6]
= 10 + 2
= 12
So, 16 – 4 = 12.
6. Complete
the subtraction sentences.
(a) 8 – 3 = 5. (b) 7- 5 = 2
18 – 3 = 🟦. 17 – 5 = 🟦.
Solution:
(a) 8 – 3 = 5. (b) 7- 5 = 2.
18 – 3 = 15. 17 – 5 = 12.
7. Subtract 4 from 12.
Solution:
12 – 4 =
8.
[12 – 4 = 10 + 2 – 4 =
2 + 10 – 4 = 2 + 6 = 8]
8. Complete the subtraction sentences.
(a) (b)
10 – 6 = 4. 10 – 7 = 3.
11 – 6 = 🟦. 11 – 7 = 🟦.
12 – 6 = 🟦. 12 – 7 = 🟦.
15 – 6 = 🟦. 15 – 7 = 🟦.
Solution:
(a) (b)
10 – 6 = 4. 10 – 7 = 3.
11 – 6 = 5. 11 – 7 = 4.
12 – 6 = 6. 12 – 7 = 5.
15 – 6 = 9. 15 – 7 = 8.
9. Add 8 and
3.
Solution:
8 + 3 = 11.
[Count from 8 and go to
next 3 steps: 9,10,11]
10. Complete
the addition sentences:
(a) 9 + 2 = 🟦. (b) 9 + 3 = 🟦.
(c) 15 + 1 = 🟦. (d) 17 + 2 = 🟦.
Solution:
(a) 9 + 2 = 11. (b)
9 + 3 = 12.
(c) 15 + 1 = 16. (d) 17 + 2 = 19.
11. Subtract 2 from 11.
Solution:
11 – 2 = 9
[count backwards from
11: 10, 9]
12. Complete the
subtraction sentences.
(a) 11 – 3 = 🟦. (b) 12 – 3 = 🟦.
(c) 14 – 1 = 🟦. (d) 18 – 2 = 🟦.
Solution:
(a) 11 – 3 = 8. (b)
12 – 3 = 9.
(c) 14 – 1 = 13. (d) 18 – 2 = 16.