Sometimes brackets are put around negative numbers to make
them easier to read, e.g. (-2). Other times a '+' or '-' sign is written in
front of the number. Both methods are used and you need to be happy using both.
If a number is positive, the + is usually missed out before the number. So 3 is
really (+3) or +3.
Adding and multiplying combinations of positive and negative
numbers can cause confusion and so care must be taken.
Addition and Subtraction
When adding and subtracting directed numbers there are a
couple of rules you can use to help you work out the answer:
- Two 'pluses' make a plus - so if two '+' signs are written next to each other you can replace them with a single '+' sign.
- Thus -3 + (+2) = -3 + 2 = -1
- Two 'minuses' make a plus - so if two '-' signs are written next to each other, you can replace them with a single '+' sign.
- Thus 6 - (-2) = 6 + 2 = 8
- A plus and a minus make a minus - so if one of each sign sit next to each other, then you can replace them with just a '-' sign.
- Thus -4 - (+3) = -4 - 3 = -7 and 3 + (-7) = 3 - 7 = -4
Basically when adding and subtracting directed numbers different
signs next to each other mean subtract, the same signs next to each other means
add.
Here there are again three simple rules to follow:
- If two positive numbers are multiplied together or divided, the answer is positive.
- Thus 2 x 4 = 8 and 10 ÷ 2 = 5
- If two negative numbers are multiplied together or divided, the answer is positive.
- Thus (-2) x (-4) = 8 and (-10) ÷ (-2) = 5
- If a positive and a negative number are multiplied or divided, the answer is negative.
- Thus (-2) x 4 = (-8) and 10 ÷ (-2) = (-5)
So basically, when multiplying or dividing two
numbers, if your numbers have the same sign the answer is positive, but
if the two numbers have different signs the answer is negative.
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