Lesson Plan - Get It!
Do you feel confident solving 2 + 2? Chances are 2 + 2 is one of the first addition problems you learned. But is 2 + 2 the same as –2 + -2? What about –2 + 2? How do those signs affect things in addition? This lesson is a reminder of just that.
Every single day, we have the opportunity to add things together.
Whether you are trying to decide the total amount of something you have, or how many of something you need, chances are that addition is involved. Because of this, it is a skill we are generally pretty good at! However, the one area we often need to review is dealing with positive and negative sign rules.
This lesson focuses on positive and negative sign rules, so by the end you can declare that you are AMAZING at all types of ADDITION.
Let's get started!
Sign rules for addition
- Positive + Positive = Positive (Add numbers, keep sign positive)
- Negative + Negative = Negative (Just add the numbers, bring along the negative sign)
- Negative + Positive = ? (Ignore the signs and SUBTRACT the numbers [largest – smallest] and keep the sign of the "bigger" number)
Let's take a look at some specific examples:
Positive + Positive = Add and stays positive
2 + 2 = 4; 3 + 10 = 13; 4 + 8 = 12
Negative + Negative = Add and stays negative
-2 + -10 = -12 (NOTICE: If both signs are the same, add the numbers together and keep their sign. In this case, when you add 2 + 10, you get 12, and keep the answer negative, because both numbers given were negative.)
-8 + -3 = -11 (8 + 3 = 11; Keep the negative sign to get –11 as an answer)
Different signs (Negative + Positive or Positive + Negative)
These problems take just a little bit of extra work, but really aren't too bad. They actually end up just becoming subtraction problems! Here are the rules:
- If given different signs when adding, you want to first ignore the signs all together (sounds silly I know, but it works, I promise!).
- Subtract the larger number minus the smaller number and write the answer.
- Decide what sign your answer should be by looking at the sign of the larger number in the original problem. If it was originally positive, your answer will be positive. If it was originally negative, the answer will be negative.
Take a few minutes to watch this Addition of Integers With Different Signs by morgankenneth12 video (below) for plenty of examples showing these steps:
Once you've watched the video, take a minute and turn to a parent or teacher and restate two addition rules that were demonstrated in the video.
Once you are done discussing, you can jump to the Got It? section to try some problems on your own.