Math 1A Singapore-Addition and Subtraction-Chapter 6.2

addition and subtraction, how many balls are there, add by making 10 first, complete the addition sentences, complete the subtraction sentences,

Addition and Subtraction


How many balls are there altogether?

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..             .
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à Make 10 first and count extra balls.

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..

10 + 3 = 13.

So, there are 13 balls altogether.

Now,


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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.

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