Step by step
The question
Question: Sam owes $25 and is paid $18.
How much does he have now?
1 Write it as a sum
We start at −25.
Is paid means up: add 18.
−25 + 18
Money we have is positive.
Money we owe is negative.
Sam owes $25: that is −25
is paid 18 → + 18
2 Work it out
Start at −25.
Go up 18.
Careful!
Sam spends more than Sam has.
The balance goes below zero.
Careful: not $18 − $-25 = $7 ✗
We land on −$7.
= −$7
So the answer is −$7: Sam owes $7.
3 Check
Let's check: go back.
−7 minus 18 is −25, where we started.
So the answer is right!
−7 − 18 = −25
Let's look back.
First: write it as a sum.
Then: work it out.
Last: check.
Answer
= −$7