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# Multiplying numbers with different signs

Find the product of numbers with different signs. Created by Monterey Institute for Technology and Education.

Video transcript

Find the product 4 times
negative 5 times negative 7.5. So we're just multiplying
three numbers right here, some are positive,
some are negative. We could actually do
this in any order, but let's just go left to right. So let's start with the
4 times the negative 5. And then we'll multiply
whatever we get there times negative 7.5. So let's just
rewrite the problems. We have 4 times negative
5, times negative 7.5. I really don't have to
write that dot there. If you just have 4 and then
in parentheses a negative 5, that means 4 times negative 5. Now, the first thing
you need to realize is that a positive
times a positive is obviously a positive. A positive times a negative,
or a negative times a positive, when you have
different signs, you're going to end up with a negative. If you have same signs, even
if you have a negative times a negative, you're going
to have a positive as well. So let's just work that
out in this problem. So you have 4 times negative 5. 4 times 5 would be 20. Let me do this in
a different color. So 4 times 5 would be 20. But we have a positive
times a negative, so it's going to be a negative. Different signs mean we're
going to have a negative. So it becomes negative
20 times negative 7.5. So let's figure
out what that is. We have to multiply
20 times 7.5. We could do that out here. So 7.5 times 20. 0 times 5 is 0. 0 times 7 is 0. Put a 0 here, because
we're obviously not going to multiply by 2. We're actually
multiplying by 20. So 2 times 5 is 10. 2 times 7 is 14, plus 1 is 15. And we get a 0, we
get a 0, we get a 5. I'm just adding here. You get a 1. And then you count
the numbers you have behind the decimal point. We only have one digit
behind the decimal point in both numbers. So you only go one digit
behind the decimal point in our product. So the answer here is 150. So this is equal to 150. And now we just have
to think about is it going to be
positive or negative. We have a negative
times a negative. They are the same sign. So it's going to result
in a positive number. So our final answer is 150. And if we actually wanted
to keep the precision here, we could write 150.0.