…understand
negative numbers
Negative numbers are used to show when something is less than zero. For
example:
•
a temperature that is ‘below freezing’
•
being overdrawn at the bank and owing money
•
company profit-and-loss accounts.
Reading negative numbers on scales of equipment
A number scale does not have to stop at zero. It can be extended to the
left by including negative numbers:
We have shown where the numbers -3 and -1 occur on the line.
A thermometer in a freezer shows a reading below zero. To work out the
temperature, you:
•
find the zero point on the thermometer
•
count the number of units away from the zero point to find the
indicated temperature
•
write down the figure, and include the ‘–‘ symbol to indicate a negative
number if it’s below the zero point.
Calculations using negative numbers
The overnight temperature in a ski resort recorded a low of –3oC. If during
the morning the temperature rose by 5 oC, what temperature would the
thermometer show?
•
From –3 to zero is 3 plus 2 to make up the 5
•
The temperature would be 2 oC.
Similarly, if the temperature fell from 3 oC to –2oC, this would be a fall of
5oC.
Try this!
•
Jane is overdrawn by £50. She puts a cheque for £70 into her account.
How much does she now have in her account?
•
The overnight low temperature in a resort was -5 oC. By noon the
temperature had risen by 8 oC. What was the temperature at noon?