Percentage of a number using mental math. Learn how to solve percent problems in your head! Since 10% is 1/10, and it's so easy to find 1/10 of any number, we can use that to quickly calculate certain percentages of quantities in our heads. to find 20% of a number, first find 10% of it, and double that.
It isn't easy really but you can always divide the number out. For example 50% of 200 is 100 by dividing 200 by 2 or 25% of 100 is 25 by dividing 100 by 4 since 25% is equivalent to 1/4
