# Solving Problems With Proportions

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We will let variable x represent this unknown quantity in our proportion.

Substitute: Now we can substitute these values into our proportion.

The percent is the unknown quantity in this problem. Identify: The phrase 8 is means that 8 is the part.

The phrase what percent tells us that percent is the unknown quantity.

and we found the solution by substituting into a proportion.

## Solving Problems With Proportions

But how would we solve this problem: 18 is 40% of what number? Identify: The phrase 18 is means that 18 is the part.

$$a=r\cdot b\Rightarrow Percent=Rate\cdot Base$$ Where the base is the original value and the percentage is the new value.

Example 47% of the students in a class of 34 students has glasses or contacts.

becomes Solve: Cross multiply and we get: 40x = 18(100) or 40x = 1800 Divide both sides by 40 to solve for x and we get: x = 45 Solution: 18 is 40% of 45 Problem 3: What is 20% of 45?

Identify: The phrase what is means represents the part and is the unknown quantity.

## Comments Solving Problems With Proportions

• ###### Proportion - Solving Proportions - Math Help

Students learn to solve proportions using cross products. For example, to solve the proportion 9/15 = 6/d, remember that the cross products of a proportion must be equal, so 9 x d = 15 x 6, or 9d = 90, and dividing both sides by 9, d = 10.…

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Cross product is usually used to solve proportion word problems. If you do a cross product, you will get 4 × x = 3 × 8 4 × x = 24. Since 4 × 6 = 24, x = 6…

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The pre-algebra concept of proportions builds upon knowledge of fractions, ratios, variables and basic facts. Solving proportions requires finding the unknown numeric value of a variable within a set of ratios that are being compared.…

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Note that in Problem 1 we did not have to cross multiply to solve the proportion. We could have used equivalent fractions instead i.e. since 20 multiplied by 5 equals 100, we get that 8 multiplied by 5 equals x, so x equals 40.…

• ###### Proportions Word Problems Worksheet and Answers

A proportion is a set of 2 fractions that equal each other. This article focuses on how to use proportions to solve real life problems.…