NUMBERS: Adding & Subtracting Signed Numbers

​NUMBERS

Adding & Subtracting

Negative and Positive Numbers​

Joezego Grande-Juko

Lesson Objectives

​By the end of this lesson, you should...

• Know how to calculate operations using negative and positive numbers.

• Know how to calculate basic BIDMAS operations. (BID)

• Complete Classwork One In Books

POSITIVE NUMBERS

A positive number is any number that represents more than zero of anything.​

In 3+2, which is the positive number?

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It is both. 3 and 2 are both positive but how do we know this. If a number has a plus sign in front of it, then it is positive. Also, if a number has nothing in front of it, it is positive. 3 has nothing in front so it is positive. 2 has a + in front of it so it is positive.

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The plus sign (+) means to add something. So we can understand it by saying if 3 oranges have been put in an empty basket, and i add 2, how many oranges do I have.​​

​QUICK QUIZ

21 +16 +14​​

In this operation, which ones are the positive number?

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Daniel says that 21 is positive. Cathy says he is wrong because there is no + in front of 21, who is right and why?

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In order to get the answer, what must we do?​​

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21 +16 +14​​

In this operation, which ones are the positive number?

​They are all positive.

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Daniel says that 21 is positive. Cathy says he is wrong because there is no + in front of 21, who is right and why?

​Daniel is right because if there is no sign in front of the number it is positive.

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In order to get the answer, what must we do?​

YES! We must start by adding 21 to 16 and whatever we get, we add 14 to it.​

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​QUICK QUIZ

​NEGATIVE NUMBERS

​Negative numbers are numbers that have a minus sign as a prefix.​ The negative sign tells you how far away the number is from the zero or any given number to subtract from.

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For instance, on your Class Dojo. When someone does something bad, teachers take out points and you end up getting a negative number. Let's sayI had 10 points and they gave me negative 5, will my new point be a negative or positive number? It will be a positive because we are simply doing 10-5 which is 5. Say I had 0 points and they gave me a negative 5, will my new points be negative or positive? It will be negative since if any number is subtracted from 0, you get the negative of that number.​

​NEGATIVE NUMBERS

​Subtract means to remove and negative numbers mean numbers we remove. So if I have 20-5, which is the negative number?

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Many would argue that it is 20 and some would say 5. The correct answer is 5. Why?

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This is because the negative sign is in front of five and since there is no sign in front of 20, it is positive. REMEMBER! 5 is taking itself out of 20. So it is the negative number.

​QUICK QUIZ

25 -6 -1​​

In this operation, which ones are the negative numbers?

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Nathan says that 25 is negative.

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In order to get the answer, what must we do?​​

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25 -6 -1​​

In this operation, which ones are the negative numbers?​

​-6 and -1 are negative numbers.

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Daniel says that 25 is negative.

​Nathan is wrong because 25 has no sign meaning it is positive.

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In order to get the answer, what must we do?​​

We must start by taking out 1 from 6 and then removing that number from 25.​

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​QUICK QUIZ

​CALCULATING NUMBERS

If we have 21+13+2, we need to start adding from the back number.​ So we add 2 to 13 which will be 15, then we add 15 to 21 which is equal to 36.

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Same applies for subtracting. If I have 34-10-6, we start from the back. I subtract 6 from 10 making 4. Then I subtract 4 from 34 making 30. If we do it the other way round, we might not get the same answer. For example, let's say i subtract from the front. I take 10 out of 34, it becomes 24 and then I take 6 out, it becomes 18. Which is wrong.

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So always start from behind and work your way up.​

​The number zero is neither positive nor negative. Positive and negative numbers are sometimes called signed numbers.

​HINT PAGE

Multiple Select

Which ones are positive? (More than one answer)

• -23

• 23

• 0

• +34

• 1200

Multiple Select

Which are wrong statements? (More than one answer)

• +0

• 0

• -0

• 8-0

Open Ended

Write this in words (Separate them with commas):

-28, -10, 0, 23, 45

Multiple Select

Which are negative? (More than one answer)

• negative two hundred

• 0

• -31

• 9

• -1150

Thank You!

By Joezego​