Mulitiplication of Positive & Negative Numbers

Common Core Standard 7ns.2.b

Help, when I multiply or divide positive and negative integers I don’t know if the answer is positive or negative.

Fortunately there are rules to help with this. Two quick and easy ways to remember the rules. 

multiply negative positive numbers

Method 1

Negatives always come in pairs.

Method 2

” Same signs = positive “
“Different signs = negative”

multiply positive negative numbers

Here are a few examples of multiplying positive and negative numbers.

-4×5= -20

5 x -2= -10

-8x-3 = 24

Multiplying a negative number by zero
Whenever you multiply a number by zero your answer will be zero. Regardless if the number is positive or negative, the answer is zero.

For example:
3 x0 = 0
-5 x 0 = 0
-456 x 0 =0

Multiplying negative numbers and exponents
Whenever you have a negative base and an exponent you need to be on the lookout for parenthesis.
If you have a negative base and parenthesis, the parenthesis applies to the base. An example will help.

( -6^2) = -6 * -6 =36
compare this to
-6^2 = -6 * 6 = -36

-4^2 = -4*4= -16
compare this to
(-4^2) = -4 * -4 = 16

Remember

**Same signs  = Positive

Different signs = Negative

Multiplying Negative Numbers and Fractions

Remember our rules for multiplying positive and negative numbers?

These same rules apply to fractions. For example:

(-1/6) * 2/3 = -2/18 = -1/9

(-1/6) * (-2/3) = 1/9

1/6 * 2/3 = 1/9

** Negatives come in pairs