Ratios, Proportions, and Percents for CBEST Exam Study Guide
Ratios and proportions, along with their cousins, percents, are sure to appear on the CBEST. A good understanding of these topics can help you pick up valuable points on the math section of the test.
The Three-Step Ratio
The three-step ratio asks for the ratio of one quantity to another.
Sample Three-Step Ratio Question
Use the three steps to help you work out the following problem.
- Which of the following expresses the ratio of 2 yards to 6 inches?
- One yard is 36 inches, so 2 yards is 72 inches. Thus, the ratio becomes 72:6. (The quantities can also be put in yards.)
- This ratio can be expressed as or 72:6. In this problem, 72:6 is the form that is used in the answers.
- Since the answer is not there, reduce. 72 inches:6 inches = 12:1. The answer is choice e. Notice that choice c, 1:12, is backward, and therefore incorrect.
Three Success Steps for Three-Step Ratios
- Put the quantities in the same units of measurement (inches, yards, seconds, etc.).
- Put the quantities in order and in the form given by the answer choices.
- If the answer you come up with isn't a choice, reduce.
Try the three steps on the following problems.
- Find the ratio of 3 cups to 16 ounces.
- Find the ratio of 6 feet to 20 yards.
- Find the ratio of 2 pounds to 4 ounces.
- In a certain class, the ratio of children who preferred magenta to chartreuse was 3:4.What was the ratio of those who preferred magenta to the total students in the class? Hint: Add 3 and 4 to get the total.
- You can eliminate two of the choices for question 2 immediately. You know that 3:16 or 16:3 can't be right because the units haven't been converted yet.
- In question 3, choices b and c are the same ratios. There can't be two right answers, so they can be eliminated. Six feet is two yards. Reducing 2:20 makes 1:10.
Four Success Steps for Four-Step Ratios
- Label the categories of quantities in the problem to illustrate exactly what you're working with.
- Set up the complete set in ratio form.
- Set up the incomplete set in ratio form.
- Cross multiply to get the missing figure.
- In a certain factory, employees were either foremen or assembly workers. The ratio of foremen to assembly workers was 1 to 7.What is the ratio of the assembly workers to the total number of employees?
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