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# Ratios, Proportions, and Percents for CBEST Exam Study Guide (page 4)

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Updated on Mar 23, 2011

#### Sample Finding Part of a Whole Question

1. In a certain laboratory, 60%, or 12, of the mice worked a maze in less than one minute. How many mice were there in the laboratory?

Once again, follow the eight Success Steps to solving this problem.

1. Twelve is part of the total number of mice in the laboratory. Sixty is the percent, which is more than half. Twelve must be more than half of the whole.
2. There are no pronouns.
3. The problem is asking, "60% of what number (total mice) is 12?"
4. Is is the verb. The 12 is all by itself on the right of the verb. What number is next to the of. The 12 goes on top, the variable on the bottom.
5. The 60 goes over 100.
6. The two fractions are equal to each other.
7. =

8. Solve.
9. There were 20 mice in the laboratory.

#### Sample Percent Question

1. Courtney sold a car for a friend for \$6,000. Her friend gave her a \$120 gift for helping with the sale. What percent of the sale was the gift?

1. The number 6,000 is the whole and 120 the part.
2. There are no pronouns, but there are words that stand for numbers. In the question at the end, the sale is 6,000 and the gift is 120.
3. The question is written out clearly: "What percent of 6,000 (sale) was 120 (gift)?"
4. Was is the verb. The number 120 is by itself on one side. It is the part, so it goes on top; 6,000 is near the of and is the whole, so it goes on the bottom.
5. There is no percent, so x goes over 100.
6. The two equal each other.
7. =

8. Solve.
9. The gift was 2% of the sale.

#### Sample Percent Change Question

A change problem is a little bit different than a basic percent problem. To solve it, just remember that change goes over old:

1. The Handy Brush company made \$500 million in sales this year. Last year, the company made \$400 million. What was the percent increase in sales this year?

First of all, what was the change in sales? Yes, 100 million. You got that by subtracting the two numbers. Which number is the oldest? Last year is older than this year, so 400 is the oldest. Therefore, 100 goes over 400.

The percent is the unknown figure, so a variable is placed over 100 and the two are made equal to each other. Cross multiply and solve for x.

#### Three Success Steps for Algebra Problems

In order to make a problem less confusing, try the WHO method:

1. What numbers are on the same side as the variable? There are two sides to the equal sign, the right side and the left side.
2. How are the numbers and the variable connected?
3. The Opposite is what? For example, the opposite of subtraction is addition.

#### Sample Interest Question

1. How much interest will Jill earn if she deposits \$5,000 at 3% interest for six months?

Interest is a percent problem with time added. The formula for interest is I = PRT. I is the interest. P is the principal, R is the rate or percent, and T is the time in years. To find the interest, you simply multiply everything together. Be sure to put the time in years. You may change the percent to a decimal, or place it over 100.

\$5,000 (principal) × 0.03 (percent) × (year) = \$75.