Addition and Subtraction

Here are the two steps to systematically do addition and subtraction.
By following these two simple steps, we will be able to evaluate all addition and subtraction mathematics expression.

1. Find out all the terms and signs in the expression:

Example :
-7+8

The terms identified here are -7 and +8

For term [-7] => sign is '-', number is '7'
For term [+8] => sign is '+', number is '8'

2. Proceed with two terms and compare the signs of the terms.

Check if the two terms have the same sign?
If SAME :
=> Final number is the sum of the two numbers
=> Final sign is the sign of the two terms

If DIFFERENT:
=> Final number is the difference between the two numbers
=> Final sign is the sign of the bigger number


Example 1:
-7+8

Is the sign for the two terms the same? [-7] and [+8]
Ans : No.

What is the difference between the two numbers 7 and 8?
Ans : 1

What is the sign of the bigger number (-7 and +8)?
Ans : +

Result of -7 +8 = +1
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Lets work through more examples.

Example 2:
-2-9

1. The terms are [-2] and [-9]

For term [-2] => sign is '-', number is '2'
For term [-9] => sign is '-', number is '9'

2. Compare [-2] and [-9].

Are the two terms having the same sign?
Ans : Yes

=> Final number is sum of 2 and 9, which is 11
=> Final sign is '-'

Result of -2 -9 = -11
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Example 3:
-5+10

1. The terms identified are [-5] and [+10]

For term [-5] => sign is '-', number is '5'
For term [+10] => sign is '+', number is '10'

2. Compare the two terms [-5] and [+10]

Are the two terms having the same sign?
Ans : No.

=> Final number is difference of 5 and 10 , which is 5
=> Final sign is the sign of the bigger number. In this case, the bigger number is 10, sign is '+'

Result of -5 +10 = +5
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Example 4:
6-18

1. The terms identified are [+6] and [-18]

For term [+6] => sign is '+', number is '6'
For term [-18] => sign is '-', number is '18'

2. Compare [+6] and [-18].

Are the two terms having the same sign?
Ans : No.

=> Final number is the difference of the two number 6 and 18 , which is 12
=> Final sign is the sign of the larger number. In this case, the sign of the larger number is '-'

Result of 6-18 = -12
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To help visualize the flow: