[The narrator reads out the onscreen text.]

NARRATOR: Question two. Use each of the following rules to calculate the amount of medicine a 4-year-old child weighing 17 kilograms needs if the adult amount is 600 milligrams. Part a. Young's rule - which uses the age of the child. The child's amount is equal to the adult amount multiplied by the age of the child divided by the age of the child plus 12. Part b. Clark's rule - which uses the weight of a child. The child's amount is equal to the adult amount multiplied by the child's weight in pounds divided by 150, or the adult amount multiplied by the child's weight in kilograms multiplied by 2.2 and divided by 150. Part a. Young's rule requires us to know the adult amount - which is given as being 600 milligrams - and also the age of the child - which is given as being 4 years. We can now substitute this information into the formula and we find that the adult amount - which is 600 milligrams - is multiplied by the age of the child - which is 4 years - divided by the age of the child - which is 4 years - plus 12. So we have 600 multiplied by four-sixteenths, which is 600 multiplied by a quarter, which gives 150 milligrams. Part b. Clark's rule. This time we need to identify the adult amount and the child's weight. The adult amount is 600 milligrams and the child's weight is 17 kilograms. Given that the weight is in kilograms, we must use the second version of the formula. So we have 600 multiplied by the child's weight - which is 17 - multiplied by 2.2 and divided by 150. This gives 149.6 milligrams.