Answer: The usual dose for an 18-month-old weighing 21 pounds is 48 mg of ibuprofen.
Step-by-step explanation: To find the usual dose of ibuprofen for a child, we need to follow these steps:
- Convert the child’s weight from pounds to kilograms. One pound is equal to 0.4536 kilograms, so we multiply 21 by 0.4536 to get 9.5256 kilograms.
- Multiply the child’s weight in kilograms by the dose per kilogram. The dose per kilogram is 5 mg when the fever is under 102.5 degrees Fahrenheit, so we multiply 9.5256 by 5 to get 47.628 mg.
- Round the result to the nearest milligram. To round a number to the nearest milligram, we look at the digit after the decimal point. If it is 5 or more, we add one to the digit before the decimal point and drop the rest. If it is less than 5, we keep the digit before the decimal point and drop the rest. In this case, the digit after the decimal point is 6, which is more than 5, so we add one to the digit before the decimal point and drop the rest. The result is 48 mg.
Therefore, the usual dose for an 18-month-old weighing 21 pounds is 48 mg of ibuprofen. Hope this helps, and have a great day! =)