Step by step
The question
Question: Mia owes $8 and spends $12.
What is her balance?
1 Write it as a sum
We start at −8.
Spends means down: take away 12.
−8 − 12
Money we have is positive.
Money we owe is negative.
Mia owes $8: that is −8
spends 12 → − 12
2 Work it out
Start at −8.
Go down 12.
Careful!
Mia spends more than Mia has.
The balance goes below zero.
Careful: not $12 − $-8 = $20 ✗
We land on −$20.
= −$20
So the answer is −$20: Mia owes $20.
3 Check
Let's check: go back.
−20 plus 12 is −8, where we started.
So the answer is right!
−20 + 12 = −8
Let's look back.
First: write it as a sum.
Then: work it out.
Last: check.
Answer
= −$20