We've got two different signs here. A negative times a positive gives us a negative answer.
Since 4 × 25 = 100, throwing a negative in the mix gives us:
(-4) × 25 = -100
Example 2
What is (-8) × (-9)?
Why hello there, double negatives. When we multiply two negative numbers together, we get a positive product. Just multiply the numbers together like normal, then drop the negative signs.
(-8) × (-9) = 72
Example 3
What is 36 ÷ (-12)?
That handy chart from the reading tells us that a positive divided by a negative gives us a negative answer, 'cause the signs are different. So divide 'em like normal, then make the answer negative.
36 ÷ (-12) = -3
Example 4
What is (-1)(-4)(5)?
Multiplying the first two factors of (-1) and (-4), we get positive 4 (the signs are the same so it's positive).
(-1)(-4)(5) = (4)(5)
Now we can multiply this 4 by the remaining factor of 5. They're both positive, so we'll get a positive product.