Lesson 2 — Activity 3: Subtracting Integers
Completion requirements
Lesson 2 — Activity 3: Subtracting Integers
Getting Ready
Just like in the previous activity, the subtraction of integers can also be done in a variety of ways, such as using a number line or a calculator.
In this activity, you will learn how to subtract positive and negative integers.
Courtesy of Pixabay
Courtesy of Pixabay
The temperature in Hinton, Alberta was 8 degrees in the morning and dropped 13 degrees by the evening. What is the evening temperature?
8 – 13 = ?
You can use your calculator or check the thermometer to figure out the evening temperature.
Look at the thermometer below. What temperature did it drop to?
Courtesy of ADLC
The temperature dropped to –5 degrees.
When you have a question like 8 – 13, you might want to turn the equation around to make it simpler, as in 13 – 8. However, this is incorrect. The actual question is asking you to take the number 8 and subtract 13 (which we know we cannot do because if
you have 8 of something, you can't take away 13 of something). However, now that you know about positive and negative integers, this question makes sense because now you can take 13 away from 8, the only difference is that you will end up
with a negative number, as the thermometer above shows you!
You have just subtracted two positive integers. So, what happens when we subtract a positive integer from a negative integer?
The temperature in Hinton, Alberta was –10 degrees in the morning and dropped by 13 degrees in the evening. What is the evening temperature?
–10 – 13 = ?
You can use your calculator or check the thermometer below to figure out the evening temperature.
Look at the thermometer below. What temperature did it drop to?
When you have a question like 8 – 13, you might want to turn the equation around to make it simpler, as in 13 – 8. However, this is incorrect. The actual question is asking you to take the number 8 and subtract 13 (which we know we cannot do because if
you have 8 of something, you can't take away 13 of something). However, now that you know about positive and negative integers, this question makes sense because now you can take 13 away from 8, the only difference is that you will end up
with a negative number, as the thermometer above shows you!
Courtesy of ADLC
The temperature dropped to –23 degrees.
Try this interactive video. You will be asked a multiple choice question within the video:
When dealing with integers, it is important to remember the following rules:
Rule #1: When subtracting, two like signs become a positive sign.
Example: – (–) (two like signs)
6 – (–3) -> 6 + 3 = 9
Rule #2: When subtracting, two unlike signs become a negative sign.
Example: – (+) (two unlike signs)
8 – (+2) -> 8 – 2 = 6
Courtesy of ADLC
Courtesy of ADLC
Follow these steps to subtract integers using a number line:
Here is one more way that might help you remember how to subtract integers:
Courtesy of ADLC
Self-check!
Try this!
The thermometer reads –6 degrees. You hear on the radio that it will drop 2 degrees overnight. What temperature will it drop to?
–8 degrees
What temperature is colder: –10 degrees or –12 degrees?
–12 degrees
Which temperature would a freezer likely be at: +5 degrees or –5 degrees?
–5 degrees
What would the temperature be if it is –10 degrees right now and it drops another 11 degrees by 4:00 this afternoon?
–21 degrees
Digging Deeper
Click here to download a document that will show you how to subtract integers using a calculator.
Click on the Play button below to watch a video on how to subtract integers.