Find the difference.
15 - (-5) =

 20

Explanation:

The two negatives cancel to form a positive. A negative is just opposite. So we have two opposites canceling.

15 - (-5) = 15 + 5 = 20

Here's another way to look at it:

Let's say we're on the 15th floor of a skyscraper. We can think of each floor of the skyscraper as part of a vertical number line (or ruler).

If we go up 5 floors, then we write 15+5 = 20 showing we end up on the 20th floor.

If we go down 5 floors, then we write 15-5 = 10

Adding makes us go up, subtracting makes us go down.

If we add on a positive number, then we go up, but adding on a negative number ultimately has us go downward.

This is because of something like 15 + (-5) = 15 - 5 = 10.

Subtracting a negative is really the same as adding. Subtracting pulls us down, but the negative counterbalances things to go the opposite direction (going up). So that's why 15-(-5) = 15+5 = 20.

Yet another way to look at it:

Negative values are useful in finance when talking about debt.

If you have 5 iou's of debt, then we write this as -5

If you transfer that debt to a friend whos account balance is $15, then their balance becomes 15 + (-5) = 10 dollars. They would have 10 dollars left after paying the debt.

Now let's say the friend got those iou's taken away and someone else paid for them. That would mean we would say 15 - (-5) = 15+5 = 20 is that first friend's new balance. Effectively they got 5 additional dollars when that debt was taken off their hands.