Page 11 - Whole Numbers (Addition and Subtraction)

Instead of eight steps of 10 each, you may calculate 60 + 80 in two
bigger steps of 40 and 40, by filling up to 100:
40 40

60 70 80 90 100 110 120 130 140

You do not have to draw a number line to think like this. You can
just think of a number line and write as follows:
60 + 40 → 100 + 40 = 140

You can also use doubling to calculate 60 + 80:
Start with 60 + 60 = 120; then add 20 to make 60 + 80 = 140.

2. How much is each of the following?
(a) 80 + 70 (b) 80 + 50 (c) 70 + 60
(d) 100 − 40 (e) 50 + 70 (f) 90 + 80
(g) 70 + 90 (h) 160 − 90 (i) 70 + 80

3. What is the sum in each case?
(a) 20 + 20 (b) 200 + 200 (c) 30 + 30
(d) 300 + 300 (e) 40 + 40 (f) 400 + 400

A double can be used to make other facts.
For example, you can transfer 100 from the one 300 in
300 + 300 = 600 to the other 300:
100

300 + 300 = 600 200 + 400 = 600

You can make a different fact by transferring 200:
200
300 + 300 = 600 100 + 500 = 600

4. (a) Use 50 + 50 = 100 to make four other facts.
(b) Use 500 + 500 = 1 000 to make four other facts.

(c) Use 40 + 40 = 80 to make three other facts.
(d) Use 400 + 400 = 800 to make three other facts.

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