Answer: 12.5 grams.
Explanation:
You can find the amount of pure substance remaining by using the half-life formula:
[tex]Q_{1}=Q(\frac{1}{2})^{\frac{t}{t2} }[/tex]
Where t is the amount of time, and t2 is the half life of the substance.
Substituting our values for the variables, we get this equation:
[tex]Q_{1} = 100(\frac{1}{2})^3\\\\Q_{1} = 100(\frac{1}{8})\\\\Q_{1} = 12.5[/tex]
After 18 hours, there will be 12.5 grams of the substance remaining.
