Answer:
40 mg
Step-by-step explanation:
Given,
The prescribed dosage the medicine for an adult = 180 milligrams,
Since, the minimum age of an adult = 18 years,
So, the prescribed dosage of the medicine for 18 years old person = 180 milligrams,
Thus, the ratio of prescribed dosage of medicine ( in mg ) and age of person ( in years ) = [tex]\frac{180}{18}[/tex]
Suppose prescribed dosage of a certain medicine for a child 4 years old is x mg,
So, ratio of prescribed dosage of medicine and age = [tex]\frac{x}{4}[/tex]
[tex]\frac{x}{4}=\frac{180}{18}[/tex]
[tex]\frac{x}{4}=10[/tex]
[tex]\implies x = 4\times 10 = 40[/tex]
Hence, the prescribed dosage of a certain medicine for a child 4 years old would be 40 mg.