Adding and Subtracting

Integers“All things excellent are as difficult as they are

rare”

Spinoza

Remember numbers can be positive or negative

NO SIGN MEANS POSITIVE

• “ – ” means the number is negative

• “ + ” means the number is positive

•No sign usually means the number is really a positive number.

• Example 5 is really +5

Adding and Subtracting positive numbers is just simple addition and subtraction

Example: 2 + 3 = 5

is really saying

"Positive 2 plus Positive 3 equals Positive 5"

You could write it as (+2) + (+3) = (+5)

AND….

Example: 6 − 3 = 3

is really saying

"Positive 6 minus Positive 3 equals Positive 3" 

You could write it as (+6) − (+3) = (+3)

Balloons and Weights

This basket has balloons and weights tied to it:

1)The balloons pull up (POSITVE)

2) And the weights drag down (NEGATIVE)

Here is what adding and subtracting positive numbers looks like

You can add balloons (you are adding positive value)

THE BASKET GETS PULLED UPWARDS (POSITIVE)

Or you can take away balloons

The basket gets pulled

down

What if you add negative numbers?

You can add weights ( you are adding negative values The basket gets

pulled downwards (NEGATIVE)

What if you subtract negative numbers?

You take away weights (you are

subtracting negative values)

The basket gets pulled upwards

(POSITIVE)

So….

Subtracting a Negative made the basket GO UP!?!

So subtracting a Negative is the

same as Adding!!!!

General Rule for SUBTRACTING integers

Example

What is 6 – (-3) ?

6 – (-3) = 6 + 3 = 9

NOW…. Solve

1)14 – (-4)

2)20 – (-10)

3)15 – (-29)

And Positive and Negative Together…

Subtracting a positive

or Adding a

negative is SUBTRACTIO

N

Example

1) What is 6 – (+3) ?

6 – (+3) = 6 – 3 = 3

2) What is 5 + (-7) ?

5 + (-7) = 5 – 7 = -2

Now solve…

1. 6 + -8

2. 10 + -5

3. 35 + -55

The Rules

Two like signs become a positive sign

Two unlike signs become a negative sign

Example

+ (+):3 + (+2) = 3 + 2 = 5

- ( - ): 6 – (-3) = 6 + 3 = 9

+ ( - ): 7 + (-2) = 7 – 2 = 5

- ( + ): 8 – (+2) = 8 – 2 = 6

So, all you have to remember is

•Two LIKE signs become a POSITVE sign

•Two UNLIKE signs become a NEGATIVE sign

LET’S WATCH A VIDEO

https://www.youtube.com/watch?v=lBscLuttQq0

Exit Ticket

1) 43 – (-23)

2) 19 + - 38

3) -27 + 33

CHALLENGE:

4) -3.16 + 14

5) 13.4 – (-3.4)