You multiply both the numerator and the denominator by the number that you need to multiply the denominator by to equal 100. Then your numerator is the percent.
It is just the difference between the signs
100%-30%=70%
100%+30%=130%
to decrese by 30%, multiply by 70%
to increase by 30%, multiply by 130%
The property the applies only to addition and multiplication is the commutative property. It means that the numbers can be arranges in any order. so for example you will get the same answer whether you do
5+6 or 6+5
