Page 14 - ArithBook5thEd ~ BCC

7.

9
999
902
+9 5 0 2

8.

56320
9864
904
+6 5 0 3

9.

32000
9844
902
+4 5 0 3

10.

299 7
984 4
20 5
+5 4 9 0 8

1.2 Subtracting Whole Numbers

Another way to say that 5 + 2 = 7 is to say that 5 = 7 − 2. In words, “5 is the difference of 7 and 2,”
or “5 is the result of taking away 2 from 7.” The operation of taking away one number from another,
or finding their difference,is called subtraction. For now, we have to be careful that the number we
take away is no larger than the number we start with: we cannot have 3 marbles and take 7 of them
away! Later on, when we introduce negative numbers, we won’t have to worry about this.
We assume you remember the differences of single-digit numbers. Just to make sure, do the following
example.
Example 6. Fill in the missing squares in the digit-subtraction table below. Here’s a start: the number
in the row labelled 7 and the column labelled 2 is the difference 7− 2 = 5. The digit in the row labelled
3 and the column labelled 3 is the difference 3 − 3 = 0. (Squares that have an asterisk (∗)will be filled
in later with negative numbers.)

Page 14