Solving Percent Equations – Practice Problems

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To calculate percent equations, it’s helpful to use what you know of ratios and proportions. To solve for unknown values when calculating percent of a number equations, use the proportion: Part/whole = percent/100. Notice the second ratio is the fraction that represents a percent.

What is the part and whole? For example, if you eat 3 slices of pizza, the part you eat is equal to 3 slices and the whole pie is equal to 4 slices. To solve for any unknown value in the proportion, you can use cross product.

To use cross product, also known as cross multiplication, imagine a cross written across the proportion a/b = c/d, when there are two equal ratios making a proportion, the products of the cross values are equal, so for this example, ad = bc. Using cross product to set up an equation then use opposite operations to isolate the variable. For some equations, not all the information will be provided in percent form, so before you can set up an equation using cross product, you may have to convert fractions and decimals to percent.

Just to refresh your memory: To convert a decimal to a percent, multiply by 100 then add the percent sign. To convert a fraction to a percent, create an equivalent fraction with 100 in the denominator. To learn more about percent equations, take a look at what Richard the Mange is making in his lab.

Convert between formats to solve percent equations. CCSS.MATH.CONTENT.HSA.SSE.B.3

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Exercises in this Practice Problem
Describe how you can determine the percent of honey.
Calculate how much is $17.5~\%$ of $200~ml$.
Define the whole, the part, and the percentage.
Help Richard convert the percentage into $ml$.
Explain the meaning of percent.
Determine the percentage.