2. © 2010 The McGraw-Hill Companies, Inc. All rights reserved 2-1 McGraw-Hill Math and Dosage Calculations for Health Care Third Edition Booth & Whaley Chapter 2: Percents, Ratios, and Proportions

3. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-2 2.1 Describe the relationship among percents, ratios, decimals, and fractions. 2.2 Calculate equivalent measurements using percents, ratios, decimals, and fractions. 2.3 Indicate solution strengths by using percents and ratios. Learning Outcomes

4. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-3 2.4 Explain the concept of proportion. 2.5 Calculate missing values in proportions by using ratios (means and extremes) and fractions (cross-multiplying). Learning Outcomes (cont.)

5. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-4 Introduction An understanding of percents, ratios, and proportion is needed to prepare solutions and solids in varying amounts. Finding a missing value in a ratio or fraction proportion problem is necessary for dosage calculation.

6. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-5 Percents Provide a way to express relationship of parts to a whole. Indicated by the symbol %. Percent means “per 100” or “divided by 100”. The whole is always 100 units.

7. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-6 A number < 1 is expressed as less than 100 percent. A number > 1 is expressed as greater than 100 percent. Any expression of one equals 100 percent. 1.0 = = 100 percent Percents (cont.)

8. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-7 Convert 42% to a decimal: Move the decimal point two places to the left Insert the zero before the decimal point for clarity 42% = 42.% =.42. = 0.42 Rule 2-1 To convert a percent to a decimal, remove the percent symbol. Then divide the remaining number by 100. Example Working with Percents

9. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-8 Convert 0.02 to a percent: Multiply by 100% Move the decimal point two places to the right 0.02 x 100% =2.00% = 2% Rule 2-2 To convert a decimal to a percent, multiply the decimal by 100. Then add the percent symbol. Working with Percents (cont.) Example

10. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-9 Rule 2-3 To convert a percent to an equivalent fraction, write the value of the percent as the numerator and 100 as the denominator. Then reduce the fraction to its lowest term. Working with Percents (cont.) Convert 8% to an equivalent fraction. 8% = 2 25 Example

11. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-10 Rule 2-4 To convert a fraction to a percent, first convert the fraction to a decimal. Round the decimal to the nearest hundredth. Then follow the rule for converting a decimal to a percent. Convert 2/3 to a percent. Convert 2/3 to a decimal. Round to the nearest hundredth. 2/3 = 2 divided by 3 = 0.666 = 0.67 0.67 x 100% = 67% Working with Percents (cont.) Example

12. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-11 Practice Convert the following percents to decimals: Convert the following fractions to percents: Answer 0.14 300%Answer 3.00 14%6/8 4/5Answer 80% Answer 75% If you are still not sure, practice the rest of the exercises “Working with Percents.”

13. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-12 Percent Strength of Mixtures Percents commonly used to indicate concentration of ingredients in mixtures Solutions Lotions Creams Ointments

14. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-13 Percent Strength of Mixtures (cont.) Two categories of mixtures: Fluid Mixtures that flow Solute Solvent or diluent Solution Solid or semisolid Creams and ointments

15. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-14 Percent Strength of Mixtures (cont.) Rule 2-5 dry a.For fluid mixtures prepared with a dry medication, the percent strength represents the number of grams of the medication contained in 100 mLs of the mixture. liquid b.For fluid mixtures prepared with a liquid medication, the percent strength represents the number of milliliters of the medication contained in 100 mLs of the mixture.

16. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-15 Percent Strength of Mixtures (cont.) Determine the amount of hydrocortisone per 100 mL of lotion. A 2% hydrocortisone lotion will contain 2 grams of hydrocortisone powder in every 100 mL. Therefore, 300 mL of the lotion will contain 3 times as much, or 6 grams of hydrocortisone powder. Example

17. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-16 Percent Strength of Mixtures (cont.) Rule 2-6 dry a.For solid or semisolid mixtures prepared with a dry medication, the percent strength represents the number of grams of the medication contained in 100 grams of the mixture. liquid b.For solid or semisolid mixtures prepared with a liquid medication, the percent strength represents the number of milliliters of the medication contained in 100 grams of the mixture.

18. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-17 Percent Strength of Mixtures (cont.) Determine the amount of hydrocortisone per 100 grams of ointment. Each percent represents 1 gram of hydrocortisone per 100 grams of ointment. A 1% hydrocortisone ointment will contain 1 gram of hydrocortisone powder in every 100 grams. Therefore, 50 grams of the ointment will contain ½ as much or 0.5 grams of hydrocortisone powder. Example

19. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-18 Practice How many grams of drug are in 100 mL of 10% solution? How many grams of dextrose will a patient receive from a 20 mL bag of dextrose 5%? Answer 10 grams Answer 5 grams will be in 100 mL, so the patient will receive 1 gram of dextrose in 20 mL

20. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-19 Ratios Relationship of a part to the whole Relate a quantity of liquid drug to a quantity of solution Used to calculate dosages of dry medication such as tablets

21. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-20 Ratios (cont.) Rule 2-7 Reduce a ratio as you would a fraction. Find the largest whole number that divides evenly into both values A and B. Reduce 2:12 to its lowest terms. Both values 2 and 12 are divisible by 2. 2:12 is written 1:6 Example

22. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-21 Ratios (cont.) Rule 2-8 To convert a ratio to a fraction, write value A (1st number) as the numerator and value B (2nd number) as the denominator, so that A:B = Convert the following ratio to a fraction: 4:5 = Example

23. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-22 Ratios (cont.) Rule 2-9 To convert a fraction to a ratio, write the numerator as the 1st value A and the denominator as the 2nd value B. = A:B Convert a mixed number to a ratio by first writing the mixed number as an improper fraction.

24. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-23 Ratios (cont.) Convert the following into a ratio: = 7:12 = 47:12 Example

25. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-24 Ratios (cont.) Convert the 1:10 to a decimal. 1. Write the ratio as a fraction. 1:10 = Rule 2-10 Rule 2-10 To convert a ratio to a decimal: 1. Write the ratio as a fraction 2. Convert the fraction to a decimal (Chapter 1) Example

26. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-25 Ratios (cont.) 2. Convert the fraction to a decimal. = 1 divided by 10 = 0.1 Thus, 1:10 == 0.1 Example (cont.)

27. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-26 Ratios (cont.) Rule 2-11 Rule 2-11 To convert a decimal to a ratio: 1.Write the decimal as a fraction (see Chapter 1). 2.Reduce the fraction to lowest terms. 3.Restate the fraction as a ratio by writing the numerator as value A and the denominator as value B.

28. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-27 Ratios (cont.) 1. Write the decimal 0.25 as a fraction. 2. Reduce the fraction to lowest terms. 3. Restate the number as a ratio. 1:4 Example

29. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-28 Rule 2-12 Rule 2-12 To convert a ratio to a percent: 1.Convert the ratio to a decimal. 2.Write the decimal as a percent by multiplying the decimal by 100 and adding the % symbol. Ratios (cont.) Click for example

30. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-29 Rule 2-13 Rule 2-13 To convert a percent to a ratio: 1.Write the percent as a fraction. 2.Reduce the fraction to lowest terms. 3.Write the fraction as a ratio by writing the numerator as value A and the denominator as value B, in the form A:B. Ratios (cont.) Click for example

31. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-30 Ratios (cont.) Convert 2:3 to a percent. Convert 25% to a ratio. Examples 1. 2:3 == 0.67 2. 0.67 X 100% = 67% 1. 25% = 2.

32. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-31 Practice Convert the following ratio to fraction or mixed numbers: 5:33:4 Answer

33. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-32 Practice Convert the following decimals to ratios: 8 0.9 Answer

34. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-33 Ratio Strengths Used to express the amount of drug In a solution In a solid dosage form Equals the dosage strength of the medication Ratio First number = the amount of drug Second number = amount of solution or number of tablets or capsules 1 mg:5 mL = 1 mg of drug in every 5 mL of solution

35. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-34 Ratio Strengths (cont.) Write the ratio strength to describe 50 mL of solution containing 3 grams of drug. First number represents amount of drug = 3 grams Second number represents amount of solution = 50 mL The ratio is 3 g:50 mL Example

36. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-35 ERROR ALERT! Do not forget the units of measurement. Including units in the dosage strength will help avoid errors.

37. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-36 Practice Write a ratio to describe the following: Two tablets contain 20 mg drug Answer 5 g:100 mL 100 mL of solution contain 5 grams of drug Answer 20 mg:2 tablets

38. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-37 Writing Proportions Mathematical statement that two ratios or two fractions are equal 2:3 is read “two to three” Double colon in a proportion means “as” 2:3::4:6 is read “two is to three as four is to six” Do not reduce the ratios to their lowest terms

39. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-38 Writing Proportions (cont.) Write proportion by replacing the double colon with an equal sign 2:3::4:6 is the same as 2:3 = 4:6 This format is a fraction proportion

40. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-39 Writing Proportions (cont.) Rule 2-14 Rule 2-14 To write a ratio proportion as a fraction proportion: 1. Change the double colon to an equal sign. 2. Convert both ratios to fractions. Rule 2-15 Rule 2-15 To write a fraction proportion as a ratio proportion: 1. Convert each fraction to a ratio. 2. Change the equal sign to a double colon. Click to go to Example

41. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-40 Writing Proportions (cont.) 1.Convert each fraction to a ratio so that 5:6 = 10:12 Write as a ratio proportion. 2. 5:6 = 10:12 same as 5:6::10:12 Write 5:10::50:100 as a fraction proportion. Examples 1. 5:10::50:100 same as 5:10 = 50:100 2. 5:10::50:100 same as

42. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-41 Practice Write the following ratio proportions as fraction proportions: 50:25::10:5 4:5::8:10 Answer 4:5 = 8:10 or Answer 50:25 = 10:5 or

43. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-42 Means and Extremes Proportions are used to calculate dosages If three of four of the values of a proportion are known, the missing value can be determined by: Ratio proportion Fraction proportion The proportion must be set up correctly to determine the correct amount of medication.

44. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-43 Means and Extremes (cont.) A : B :: C : D Extremes Means A ratio proportion in the form A:B::C:D.

45. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-44 Means and Extremes (cont.) Rule 2-16 Rule 2-16 To determine if a ratio proportion is true: 1.Multiply the means. 2.Multiply the extremes. 3.Compare the product of the means and the product of the extremes. If the products are equal, the proportion is true.

46. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-45 Means and Extremes (cont.) Determine if 1:2::3:6 is a true proportion. 1.Multiply the means: 2 X 3 = 6 2.Multiply the extremes: 1 X 6 = 6 3.Compare the products of the means and the extremes: 6=6 The statement 1:2::3:6 is a true proportion. Example

47. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-46 Means and Extremes (cont.) Rule 2-17 Rule 2-17 To find the missing value in a ratio proportion: 1.Write an equation setting the product of the means equal to the product of the extremes. 2.Solve the equation for the missing value. 3.Restate the proportion, inserting the missing value. 4.Check your work. Determine if the ratio proportion is true.

48. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-47 Means and Extremes (cont.) Find the missing value in 25:5::50:? 1.Write an equation setting the product of the means equal to the product of the extremes. 5 x 50 = 25 x ? and 250 = 25? 2.Solve the equation by dividing both sides by 25. ? = 10 Example

49. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-48 Means and Extremes (cont.) 3.Restate the proportion, inserting the missing value. 25:5::50:10 4.Check your work. 5 X 50 = 25 X 10 250 = 250 The missing value is 10. Example (cont.)

50. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-49 Canceling Units in Proportions Remember to include units when writing ratios. Helps determine the correct units for the answer. 200 mg:5 mL::500 mg:? Cancel units correctly. 200 mg:5 mL::500mg:? Answer to ? will be in mL.

51. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-50 Canceling Units in Proportions (cont.) Rule 2-18 If the units in the first part of the ratio in a proportion are the same, they can be canceled. If the units in the second part of the ratio in a proportion are the same, they can be canceled.

52. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-51 Canceling Units in Proportions (cont.) If 100 mL of solution contains 20 mg of drug, how many milligrams of the drug will be in 500 mL of the solution? Example 20mg:100mL::?:500mL 20mg X 500 = 100 X ? ? = 100mg

53. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-52 Practice Determine whether the following proportions are true: 3:8::9:32 Answer True 6:12::12:24 Answer Not true

54. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-53 Practice Use the means and extremes to find the missing values. 3:12::?:36 Answer 8 10:4::20:? Answer 9

55. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-54 Cross-Multiplying Determination if true or not Proportion Compare the products of the extremes (A & D) with the products of the means (B & C) Fractions Cross-multiplying to determine if it is true A : B :: C : D Extremes Means

56. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-55 Cross-Multiplying (cont.) Rule 2-19 Rule 2-19 To determine if a fraction proportion is true: 1.Cross-multiply Multiply the numerator of the first fraction with the denominator of the second fraction. Then multiply the denominator of the first fraction with the numerator of the second fraction. 2.Compare the products. The products must be equal.

57. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-56 Cross-Multiplying (cont.) Determine if is a true proportion. 1. Cross-multiply. 2 X 25 = 5 X 10 2. Compare the products on both sides of the equal sign. 50 = 50 Therefore, is a true proportion. Example

58. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-57 Cross-Multiplying (cont.) Rule 2-20 Rule 2-20 To find the missing value in a fraction proportion: 1.Cross-multiply. Write an equation setting the products equal to each other. 2.Solve the equation to find the missing value. 3.Restate the proportion, inserting the missing value. 4.Check your work. Determine if the fraction proportion is true.

59. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-58 Cross-Multiplying (cont.) Find the missing value in 1.Cross-multiply. 3 X ? = 5 X 6 2. Solve the equation by dividing both sides by three. ? = 10 Example

60. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-59 Cross-Multiplying (cont.) 3. Restate the proportion, inserting the missing value. 4. Check your work by cross-multiplying. 3 X 10 = 5 X 6 30 = 30 The missing value is 10. Example (cont.)

61. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-60 Canceling Units in Fraction Proportions You can cancel units in fraction proportions. Rule 2-21 If the units of the numerator of the two fractions are the same, they can be dropped or canceled before setting up a proportion. Likewise, if the units from the denominator of the two fractions are the same, they can be canceled.

62. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-61 You have a solution containing 200 mg drug in 5 mL. How many milliliters of solution contain 500 mg drug? Canceling Units in Fraction Proportions (cont.) The missing value can now be found by cross- multiplying and solving the equation as before. Example Set up the fraction

63. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-62 Canceling Units in Fraction Proportions (cont.) Set up the fraction. Solve for ?, the missing value. 1.100 X ? = 20 mg X 500 2.Divide each side by 100 3.? = 100mg of drug in 500mL solution Example If 100 mL of solution contains 20mg of drug, how many milligrams of the drug will be in 500mL of solution?

64. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-63 Practice Determine if the following proportions are true: Answer Not true

65. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-64 Practice Cross-multiply to find the missing value. Answer 1

66. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-65 Practice If 250 mL of solution contains 90 mg of drug, there would be 450 mg of drug in how many mL of solution? Answer 1, 250 mL

67. © 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 2-66 End of Chapter 2 If what you're working for really matters, you'll give it all you've got. ~ Nido Qubein