ABSTRACT
Chapter 3 Per cent and percentages 220 Chapter 4 Units and equivalences 222 Chapter 5 Moles and millimoles 223 Chapter 6 Drug strengths or concentrations 227 Chapter 7 Dosage calculations 228 Chapter 8 Infusion rate calculations 250 Chapter 10 Action and administration of medicines 278
Question 1 Before attempting the calculation, first estimate the answer. The percentage is 30 which we can consider to be approximately one-third. To make the estimation easier, we will keep the number as 3,090 (as it is divisible by 3). So, we are now looking at one-third of 3,090 which is 1,030. Alternatively, we can estimate the answer by manipulation of numbers. Round down the amount to 3,000 100% – 3,000 10% – 300 (by dividing by 10) 30% – 900 (by multiplying by 3) As the amount was rounded down, then the answer will be slightly higher – 920 would be a good guess. Now we can attempt the calculation. When doing percentage calculations, the number or quantity you want to find the percentage of is always equal to 100%. So, 3.090 is equal to 100% and you want to find out how much 30% is. Calculate how much is equal to 1%, i.e. divide by 100 (you are using the one unit rule)
=1% 3,090 100
Multiply by the percentage required (30%):
= × =30% 3,090 100
30 927
Checking the calculated answer of 927 with our estimation of 920 to 1,030 means that we should be confident in our calculated answer.
