# Solving Proportions – Practice ProblemsHaving fun while studying, practice your skills by solving these exercises!

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To understand proportions, you must understand ratios. Ratios are used to compare quantities. You can write a ratio to look like a fraction. For example the ratio one to two can be written as ½.

How do ratios differ from fractions? Fractions are used to compare a part of something to the whole of that same something. Ratios compare quantities, like 3 apples for every 4 oranges. Are you wondering how all of this is connected to proportions? Two equal ratios make a proportion. Proportions are very useful to solve for unknown amounts because you can use cross product, which is also known as cross multiplication.

To use cross product, multiply the numbers that are diagonally across the equal sign. For all proportions, their cross products are always equal. Let’s consider an example. If there are 3 apples for every 4 oranges, and there are 96 oranges, how many apples are there? You can set this up as a proportion. Make sure the numbers for apples are in the same position in the fraction, as well as the numbers for the oranges. This means, be consistent with the quantities you write in the numerator and denominator. If you put apples in the numerators of one ration do so with the other. After you set up the proportion and calculate the equal cross products, use algebra to solve for the unknown quantity. FYI – there are 72 apples.

You may be surprised how useful setting up proportions and using cross product to solve for unknown amounts can be. You can use this strategy to solve all kind of problems as you progress with your studies of algebra and geometry. To learn more about proportions, watch this video.

Solve unknown quantities using proportions CCSS.MATH.CONTENT.HSA.CED.A.1

Exercises in this Practice Problem
 Manipulate the formula to get the value for $f$. Determine the depth of the snow after two hours. Solve the following proportions. Determine the number of days Freddy the yeti has to save his pocket money. Find the correct proportion. Determine the number of hours till the snow is four feet deep.