How_To_Be_Good_At_Math

NUMBERS • POSITIVE AND NEGATIVE NUMBERS 19

Ups and downs

We sometimes use positive and

negative numbers to describe

the floors in a buillding. Floors

below ground level often have

negative numbers.

REAL WORLD MATHS

NEGATIVE NUMBERS

0

POSITIVE NUMBERS

−1

We don’t usually put any sign

in front of positive numbers.

So, when you see a number

without a sign, it’s always positive.

1 2 3 4 5 6 7 8 9 10

To subtract a positive

number, move to the left

on the number line

To add a negative number, move

to the left on the number line

Move to the right to count up from zero

Zero (0) is not positive or

negative. It’s the separation

point between the positive and

negative numbers.

Subtracting a positive number

Now let’s try subtracting a positive

number. To subtract 3 from 2, we move

to the left to get the answer.

2 − 3 = −1

Adding a negative number

When we add a negative number, it

gives the same answer as subtracting a

positive one. To add −3 to 2, we move left

on the number line.

2 + (−3) = −1

Positively puzzling

Use a number line to work out

these calculations.

TRY IT OUT

7 − (−3) =?

−4 + (−1) =?

7 + (−9) =?

−2 − (−7) =?

Answers on page 319

−5 −4 −3 −2 −1 0 1 2 3 4 5

−5 −4 −3 −2 −1 0 1 2 3 4 5

-2 -1 0 1 2 3 4 5 6 7 8 9

018_019_Positive_negative_numbers.indd 19 29/02/2016 14:08