80 times 5 is 400, but what is the answer if both 80 and 5 are negative numbers? Here we will determine if the answer to negative 80 times negative 5 is positive 400 or negative 400.
There are many different ways to explain and determine if the answer to negative 80 times negative 5 is -400 or +400 using mathematical terms such as additive inverse and mathematical laws like the Distribute Law.
We will take a different approach - process of elimination: We will simply test if -400 is the correct answer using basic algebra.
We will test if -400 is correct by setting up the equation negative 80 times negative 5 equals negative 400, and then simplifying the equation to see if it is true.
(-80) (-5) = (-400)
Divide both sides of the equation by (-5) :
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| = |
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The numerator and denominator on the left side both have (-5) which even each other out and can be removed:
| (-80) = |
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The numerator and denominator on the right side both have a minus sign (-) which even each other out and can be removed:
| (-80) = |
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A numerator of 400 and denominator of 5 on the right side is the same as 400 divided by 5 which is 80. Now we end up with this untrue equation:
(-80) = (80)
-80 is NOT equal to 80, thus we have proven that negative 80 times negative 5 is not equal to -400. The answer must therefore be 400:
-80 x -5 = 400
The above applies to all math problems where you multiply two negative numbers. Multiplying two negative numbers such as negative 80 times negative 5 will always have a positive answer.
Negative Times Negative Calculator
Here you can multiply another two negative numbers together.
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