Ratios and Percents: The Basics

A ratio compares two amounts. If a bag has 6 red marbles and 9 blue marbles, the ratio of red to blue is 6 to 9. You simplify a ratio the way you simplify a fraction, by dividing both numbers by the same value, so 6 to 9 becomes 2 to 3.

A proportion says two ratios are equal. To solve one, look at how the bottom numbers are related, then do the same thing to the top numbers. Keep the same kind of amount on top on both sides.

Percent means out of one hundred. To find a percent of a number, turn the percent into a decimal by moving the decimal point two places left, then multiply, because the word of means multiply.

For a discount, find the amount that comes off first, then subtract it from the original price.