Multiply Negative Numbers

How to multiply minus numbers (negative numbers): formula, 3 examples, and their solutions.

Formula

Formula

If multiplying same signed numbers,
the result is plus.
(+)⋅(+) = (+)
(-)⋅(-) = (+)

If multiplying different signed numbers,
the result is minus.
(+)⋅(-) = (-)
(-)⋅(+) = (-)

Example 1

Example

Solution

-5 is minus.
-4 is minus.
So -5⋅(-4) is minus times minus.
So write plus.

5 times 4 is 20.
So write 20.

So +20 is the answer.
Or you can simply write 20.

Example 2

Example

Solution

3 is plus.
-7 is minus.
So 3⋅(-7) is plus times minus.
So write minus.

3 times 7 is 21.
So write 21.

So -21 is the answer.

Example 3

Example

Solution

-9 is minus.
2 is plus.
So -9⋅2 is minus times plus.
So write minus.

9 times 2 is 18.
So write 18.

So -18 is the answer.