Percentage is a commonly used word. Sales tax is a percentage of the sale price; a final examination is a certain percentage of the final grade; interest on a home mortgage represents a percentage of the balance owed; interest on a savings account is expressed as a percentage. Health care professionals see percentages written with medications (e.g., magnesium sulfate 50%). In addition to its use with medications, percentage is also used in the assessment of burns. The size of a burn (percentage of injured skin) is determined by using the rule of nines in an adult (Figure 5-1). The basis of the rule is that the body is divided into anatomical sections, each of which represents 9% or a multiple of 9% of the total body surface area. The total body surface area (BSA) is represented by 100%. Another method used is the age-specific burn diagram or chart. Burn size is expressed as a percentage of the total BSA. In children, age-related charts are used because their body proportions differ from those of an adult and the rule of nines cannot be applied.

Many health care providers use solutions that are expressed in percentages for external as well as internal use (e.g., hydrocortisone cream, lidocaine, and intravenous [IV] solutions).

In current practice, percentage solutions are prepared by the pharmacy, and people can purchase solutions or components of the solutions over the counter. Some institutions require nurses to prepare solutions in house (in the hospital) as well as in home care for clients being cared for at home. Understanding percentages provides the foundation for preparing and calculating dosages for medications that are ordered in percentages.

The term percent (%) means parts per hundred. A percentage is the same as a fraction in which the denominator is 100, and the numerator indicates the part of 100 that is being considered.

Example:

4%=4100 (4 per 100)

CHANGING PERCENTAGES TO FRACTIONS, DECIMALS, AND RATIOS

The percent sign may be used with a whole number (15%), a fraction (1/2%), a mixed number (14½%), or a decimal (0.6%).

RULE

To change a percent to a fraction, drop the percent sign, place the number over 100, and reduce to lowest terms.

Example 1:

8%=8100, reduced is 225

Example 2:

14%=14÷100=14×1100=1400

Practice Problems

Change the following percentages to fractions, and reduce to lowest terms.

9. 1% _______________________

10. 2% _______________________

11. 50% _______________________

12. 80% _______________________

13. 3% _______________________

Answers on p. 604

RULE

To change a percentage to a decimal, drop the percent sign, and move the decimal point two places to the left (add zeros as needed).

Example 1:

25% = 0.25

Example 2:

1.4% = 0.014

Example 3:

75%=75100=34 (lowest terms). Divide the numerator of the fraction (3) by the denominator (4).

0.754 )3.00

NOTE

Example 3 is an alternative method. Drop the percent sign. Write the remaining number as the numerator. Write “100” as the denominator. Reduce the result to lowest terms. Divide the numerator by the denominator to obtain a decimal.

Practice Problems

Change the following percentages to decimals. Round to two decimal places, as indicated.

14. 10% _______________________

15. 35% _______________________

16. 50% _______________________

17. 14.2% _______________________

18. 67%_______________________

Answers on p. 604

RULE

To change a percentage to a ratio, change it to a fraction, and reduce to lowest terms; then place the numerator as the first term of the ratio and the denominator as the second term. Separate the two terms with a colon (:).

Example:

10%=10100=110=1:10

Practice Problems

Change each of the following percentages to a ratio. Express in lowest terms.

19. 25% _______________________

20. 11% _______________________

21. 75% _______________________

22. 4.5% _______________________

23. ⅖% _______________________

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