Chapter 9 · Questions · page 40 of 68
Why is a negative times a negative positive?
Short answerMultiplying by a negative flips the sign. Do it twice and you are back to positive, so -6 times -4 is 24.
levelPre-algebra
standard7.NS.A.2
practiceInteger operations
Multiplying by -1 flips a number to the other side of zero. -6 × -4 is 6 × 4 flipped twice, once for each negative, which lands back on the positive side. That is why you can count negatives: even means positive, odd means negative.
How to use it
- Multiply the sizes, ignoring the signs.
- Count the negative signs in the product.
- Even count: positive answer. Odd count: negative answer.
Example
Where it goes wrong
- Using this rule for adding. -6 + (-4) is -10, not 10.
- Losing count with three or more factors. Count every negative.