Thursday, June 23, 2011

Addition and Substaction

ADDITION

Do the numbers have the SAME SIGN?
YES - Same Signs:
Find the SUM:

NO - Different signs:
Find the DIFFERENCE:
(-3) + (-6) = (-9)

(+4) + (+5) = (+9)

(+5) + (-7) = (-2)

(-4) + (+6) = (+2)

SUBTRACTION

First, change the SUBTRACTION problem to an ADDITION problem;

Then, follow the rules (above) for solving the new ADDITION problem.

(-6) - (+2) =

First, copy the problem exactly.

1. The first number stays the same.

2. Change the operation.

3. Switch the NEXT SIGN.

4. Follow the rules for addition.


(-6) - (+2) =

(-6)

(-6) +

(-6) + (-2)

(-6) + (-2) = (-8)

Subtract means:
Add the opposite.

(+2) - (-6) =
(+2) + (+6) = (+8)

Subtract means:
Add the opposite.

(-7) - (-3) =
(-7) + (+3) = (-4)
Subtract means:
Add the opposite.

(+4) - (+9) =
(+4) + (-9) = (-5)


MULTICATION OR DIVISION

First, DO the multiplication or division.

Then determine the sign:

Count the number of negative signs....

Are there an EVEN number of negative signs?
YES (an EVEN number of negative signs) the answer is POSITIVE
NO (an ODD number of negative signs) the answer is NEGATIVE

First, copy the problem exactly.


(-2) * (-4) * (-6) =

DO the multiplication or division.


|2| * |4| * |6| = |48|

Count the number of negative signs....
Determine the sign of the answer:


(-2) * (-4) * (-6) =

Are there an EVEN number of negatives?
If YES, the answer is POSITIVE
otherwise, the answer is negative.


A total of THREE NEGATIVES
Three is NOT EVEN (it's odd).
So the answer is NEGATIVE

-48

(4) ÷ (2) * (6) = 12
A total of ZERO NEGATIVES
Zero IS EVEN .
So the answer is POSITIVE



(4) ÷ (-2) * (6) = -12
A total of ONE NEGATIVE
One is NOT EVEN (it's odd).
So the answer is NEGATIVE



(-4) ÷ (2) * (-6) = 12
A total of TWO NEGATIVES
TWO IS EVEN .
So the answer is POSITIVE

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