8 times 80 is 640, but what is the answer if both 8 and 80 are negative numbers? Here we will determine if the answer to negative 8 times negative 80 is positive 640 or negative 640.
There are many different ways to explain and determine if the answer to negative 8 times negative 80 is -640 or +640 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 -640 is the correct answer using basic algebra.
We will test if -640 is correct by setting up the equation negative 8 times negative 80 equals negative 640, and then simplifying the equation to see if it is true.
(-8) (-80) = (-640)
Divide both sides of the equation by (-80) :
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| = |
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The numerator and denominator on the left side both have (-80) which even each other out and can be removed:
| (-8) = |
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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:
| (-8) = |
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A numerator of 640 and denominator of 80 on the right side is the same as 640 divided by 80 which is 8. Now we end up with this untrue equation:
(-8) = (8)
-8 is NOT equal to 8, thus we have proven that negative 8 times negative 80 is not equal to -640. The answer must therefore be 640:
-8 x -80 = 640
The above applies to all math problems where you multiply two negative numbers. Multiplying two negative numbers such as negative 8 times negative 80 will always have a positive answer.
Negative Times Negative Calculator
Here you can multiply another two negative numbers together.
What is negative 8 times negative 81?
Here is the next problem on our list that we have explained and calculated.
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