Question 1.11: A dose of 240 mg of acetaminophen is prescribed for a 20-kg ...

[1] Identify the original quantity and the desired quantity.
• We must convert the number of milligrams of acetaminophen needed to the number of mL that must be administered.

240 mg                            ? mL
original quantity           desired quantity

[2] Write out the conversion factors.

[3] Solve the problem.
• Arrange the terms so that the units in the numerator of one term cancel the units of the denominator of the adjacent term. In this problem we need to cancel milligrams to obtain milliliters.
• In this problem we are given a fact we don’t need to use— the child weighs 20 kg. We can ignore this quantity in carrying out the calculation.

[4] Check.
• The answer of 7.5 mL (not 0.75 or 75) is reasonable. Since the required dose is larger than the dose in 2.5 mL, the answer must be larger than 2.5 mL.