Coolmath Pre-Algebra
Signed Number (Integers) lesson 7 -
Addition with Different Signs
(page 1 of 7) ---- This pre-algebra lesson explains how to add
signed numbers (integers) when the signs
are different.
I'm going to use number lines
and my little math car a lot in this lesson. It's
really the only good way to get this into your head!
So, if you didn't see the
last lesson, please
check it out
now.
Before, we
did addition when all the numbers had the same sign.
Here's a quick review:
If all the numbers are
positive, then the answer is
positive.
If all the numbers are
negative, then the answer is
negative.
Note: The easy way
to do this problem is to just ignore
all the
negative signs,
add them up like positive numbers,
then stick a
negative
sign on your answer!
OK, we're cool with
that...
So... What if some of the
numbers are positive and some are
negative?
Will the answer be
positive or
negative?
It all depends on the
numbers!
Let's do some with our car
and the number lines and see how it works:
* Remember, when the
number is positive, the
car drives forward and, when the
number is negative, the
car backs up.
