ZingPath: Percent of a Quantity

To find the missing value in a proportion, we can apply the Cross Product Property.

For example, If a equals the quantity of blue paint and b equals the quantity of red paint, a + b would equal the quantity of mixed paint. Let's assume that there are 5 gallons of blue paint used (a = 5) and 10 gallons of red paint used (b = 10). The total amount of mixed paint (a + b) would be 15. If we are asked how many gallons of blue paint would be needed if we had 30 gallons of mixed paint, we could find the answer by using the Cross Product Property.

The first and last terms of a proportion are called extremes. The middle terms are called the means.

The following key vocabulary terms will be used throughout this Activity Object:

• Cross Product Property - in a proportion, the product of the means is equal to the product of the extremes In the proportion , b and c are the means and a and d are the extremes. So, as per the cross product, ad = bc. For example, If , then, 5 × 36 = 12 × 15 according to the Cross Product Property.
• proportion - an equation when it states equality between two ratios
• ratio - a comparison of two numbers or quantities For example, A baseball team won 15 out of 25 games. The ratio of total games won to total games played is .