Page 42 - Math Smart - 7
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We can also use number discs to help us carry out addition and subtraction that
involves negative numbers.
A mining engineer works
A number disc has two sides, like a coin. One side shows the positive number 1.
50 m underground. To
When we flip the disc, the other side shows the negative number 1.
attend a meeting, she
needs to go to an office
© ^ They are the inverse
that is 97 m above her
of each other.
mining site. What is the
front back
height of the office above
Since 1-1=0,
ground level?
when we put a pair of them together, we get a zero pair. 0
zero pair
Example 2
How can we work out (-3) + 6?
Let's put three discs on the table and six discs on the table.
Group the discs to see how many zero pairs we have.
same
We are left with 3. So, (-3) + 6 = 3
number
number
Work out 4- 6.
We can write it as 4 + (-5). (4) + (-6)
This is the ^ \
operation. This is the sign to indicate
the negative value.
To add a negative
integer, you move to We start from the number 4 and move 6 steps to the left. We land on the
the left on a horizontal number (-2).
number line.
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10
Therefore, (4) + (-6) = -2.
We can also use number discs to help us.
00
©0
So, 4-6 = -2.
UNIT 2 I Integers
