Evaluating formulas

Evaluating formulas

Before you start there are some simple formulas to evaluate on page 5.

Question 1

A rule to calculate the amount of medicine (mL) a child needs is:

Child amount = (Adult amount × Age of child) ÷ (Age of child + 12)

Adult amount
Age of child
Child amount
10 8  


Substitute in the formula. This formula is known as Young's rule and uses age to calculate the dosage.

Child amount  = (10 × 8) ÷ (8 + 12)(Evaluate the brackets first.)
  = 80 ÷ 20
  = 4 mL.

Check that your answer is less than the amount for an adult.