Page 14 - Whole Numbers (Addition and Subtraction)

When you know an addition fact, you can easily find two
subtraction facts.
For example if you know that 35 + 85 = 120, you also know that
120 − 35 = 85 and 120 − 85 = 35.

0 10 20 30 40 50 60 70 80 90 100 110 120

120 110 100 90 80 70 60 50 40 30 20 10 0

6. In each case give the answer, and write two subtraction facts.
Follow the above example of 35 + 85 = 120.
(a) 40 + 50 (b) 300 + 600
(c) 30 + 50 (d) 200 + 700

One way to subtract is to ask yourself what must be added to the
smaller number to make up the difference.
For example, to calculate 160 − 70 you may ask yourself what
must be added to 70 to get to 160, and first fill up to 100. It is like
finding the missing numbers in number sentences:

70 + what number? → 100 + what number? = 160
When you have found the missing numbers, you can add them to
get the final answer.
70 + 30 → 100 + 60 = 160
So, 160 − 70 = 30 + 60 which is 90.

So 160 − 70 = 90

You can also subtract piece by piece, filling up to 100 first.
For example, to calculate 130 − 80 you may think like this:
130 − 30 = 100. Now there is 50 more to subtract.
100 − 50 = 50

So, 130 − 80 = 50

The above thinking can also be described as follows:
130 − 30 → 100 − 50 = 50, so 130 − 80 = 50

13