A ratio compares two quantities. For example, if we have 5 apples and 7 bananas, the ratio is 5 to 7, written as 5:7 or as the fraction 5/7. A proportion states that two ratios are equal, like 1/2 equals 3/6. We can check this by cross multiplying: 1 times 6 equals 6, and 2 times 3 also equals 6.