More on Adding and Subtracting

Here are some examples involving temperature which illustrate the use of positive and negative integers.

Example 1

The maximum temperature in Canberra on a day during winter was $3$ degrees Celsius.

The temperature dropped $5$ degrees to its minimum.

What was the minimum temperature in Canberra that day?

$3 – 5 = ?$

Directed number line

$3 – 5 = 2$ below zero

$3 – 5 = –2$

Example 2

The minimum temperature in Canberra on another day in winter was $–2$ degrees Celsius.

The temperature rose $4$ degrees to its maximum.

What was the maximum temperature in Canberra that day?

$– 2 + 4 = ?$

Directed number line

Example 3

The temperature in Perisher valley one evening was ­$-4$ degrees Celsius. Overnight the temperature fell $2$ degrees Celsius. What was the temperature in the morning?

$– 4 – 2 = ?$ Did you get $– 6?$

Try the following questions for yourself.

$6-7=$

$-7+6=$

$3-12+10=$

$-20+5=$

$-10-20=$

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