Adding (and subtracting)
signed numbers:
- Same signs (either both
positive or both negative) -
Add the numbers and keep the same sign.
- (+) + (+) = +
5 + 3 = 8
- (-) + (-) =
- -2 + (-4) =
-6
- same as (-) – (+) = - -2
– 4 = -6 (both numbers are
considered negative)
- Opposite signs -
Take the difference between the two
numbers and the sign of the higher of
the two.
- (+) + (-) = or (+) – (+) =
3 + (-7) = -4
5
+ (-2) = 3
4
– 5 = 4 + (-5) = -1
11
– 2 = 11 + (-2) = 9
- (-) + (+)
=
-3 + 14 = 11
-9
+ 5 = -4
- Subtracting a negative
- -(-) = + like (-1) times a
negative number
- -1 times -3 equals positive
3
- (-1)(-3) = -(-3) = 3
Multiplying signed
numbers:
- Two numbers with the same
sign - Answer will be positive
- (+)(+) = + 3
(4) = 12
- (-)(-) = +
(-2)(-1) = 2
- Two numbers with opposite
signs - Answer will be negative
- (+)(-) = -
(2)(-5) = -10
- (-)(+) = -
(-3)(6) = -18
- More than two numbers
multiplied by each other:
- If an even number of negative
multiples, answer will be positive
- (-)(-)(-)(-) =
+ (-3)(-1)(-2)(-1)
= 6
- If an odd number of negatives
multiples, answer is negative
- (-)(-)(-)(-)(-) = -
(-1)(-2)(-3)(-2)(-2) = -2
Dividing signed numbers:
- Same sign - Answer
will be positive
- Opposite signs -
Answer will be negative
-
Because (-6)(-3) = 18
-
Because (3)(-4) = -12
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Because (-6)(4) = -24