Step by step
The question
Question: It is −4°C.
It warms up 9 degrees.
What is the temperature now?
1 Write it as a sum
We start at −4.
Warms up means up: add 9.
−4 + 9
Below zero is negative.
−4°C: below zero
warms up 9 → + 9
2 Work it out
Start at −4.
Go up 9.
We pass 0.
Careful!
We start at −4, not at 4.
Keep the minus sign.
Careful: not 4 + 9 = 13 ✗
We land on 5°C.
= 5°C
So the answer is 5°C: 5 degrees above zero.
3 Check
Let's check: go back.
5 minus 9 is −4, where we started.
So the answer is right!
5 − 9 = −4
Let's look back.
First: write it as a sum.
Then: work it out.
Last: check.
Answer
= 5°C