Step by step
The question
Question: Leo owes $15 and earns $40.
How much does he have now?
1 Write it as a sum
We start at −15.
Earns means up: add 40.
−15 + 40
Money we have is positive.
Money we owe is negative.
Leo owes $15: that is −15
earns 40 → + 40
2 Work it out
Start at −15.
Go up 40.
We pass 0.
Careful!
We start at −15, not at 15.
Keep the minus sign.
Careful: not 15 + 40 = 55 ✗
We land on $25.
= $25
So the answer is $25: Leo has $25.
3 Check
Let's check: go back.
25 minus 40 is −15, where we started.
So the answer is right!
25 − 40 = −15
Let's look back.
First: write it as a sum.
Then: work it out.
Last: check.
Answer
= $25