Math 1A Singapore-Addition and Subtraction-Chapter 6.2

Addition and Subtraction

How many balls are there altogether?

⚽.⚽.⚽             ⚽.⚽

⚽.⚽.⚽             ⚽.⚽

⚽.⚽.⚽

à Make 10 first and count extra balls.

⚽.⚽.⚽.⚽.⚽ ⚽.⚽.⚽.⚽.⚽

⚽.⚽.⚽

10 + 3 = 13.

So, there are 13 balls altogether.

Now,

● ●●    ● ●●    ● ●●    ● ●●    ●

à

●● ●● ●●    ● ●●    ● ●●    ●

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.