Ratio and Proportion

Introduction

Ratio and proportion is an easy, provable method of drug dose calculation. The setup of problems is logical and systematic. Answers can be proven if the setup is correct.

Ratio

A ratio indicates the relationship of one quantity to another. It indicates division and may be expressed in fraction form.

Example

⅓ may be expressed as the ratio 1:3.

WORKSHEET 2A

Answers on page 345

Expressing Ratios as Fractions

Express the following ratios as fractions reduced to lowest terms.

Proportion

A proportion shows the relationship between two equal ratios. A proportion may be expressed as 3 : 5 :: 6 : 10 or 3 : 5 = 6 : 10.

To solve the ratio and proportion problems, do the following:

Steps for Solving Ratio and Proportion Problems

1. Multiply the two inside numbers.

2. Multiply the two outside numbers.

3. Check to see that the answers are the same.

Example

Multiply the two inside numbers: 5 × 6 = 30.

Multiply the two outside numbers: 3 × 10 = 30.

Solving Proportion Problems When One of the Numbers Is Unknown, or x

Example

Multiply the two inside numbers (means).

8 × x = 8x

Multiply the two outside numbers (extremes).

2 × 24 = 48

Move the x product to the left side of the equation. It will now look like this:

8x = 48

Now you must get x to stand alone.

RULE

To solve for the value of x, divide both sides of the equation by the number next to x. Those numbers will cancel each other. The result will be that x will stand alone.

What you do to one side of the equation, you must do to the other to keep the sides equal.

Example

x = 6

How do you know your answer is correct?

RULE

To check your answer, substitute the answer for the x in the problem, multiply the inside numbers together, and then multiply the outside numbers together. The products should be equal.