ANSWER
The amount of sample left after 120 years is 21.9 grams
EXPLANATION
Given that;
The original mass of the sample is 700g
The half life of the sample is 24 years
Time is 120 years
Follow the steps below
Step 1; Write the half-life formula
[tex]\text{ N = N}_o(\frac{1}{2})^{\frac{t}{\iota}}[/tex]Step 2; Substitute the given data into the above formula
[tex]\begin{gathered} \text{ N = 700 }\times\text{ \lparen}\frac{1}{2})^{\frac{120}{24}} \\ \\ \text{ N = 700 }\times\text{ \lparen}\frac{1}{2})^5 \\ \\ \text{ N = }\frac{700}{\text{ 32}} \\ \text{ N = 21.9 grams} \end{gathered}[/tex]Therefore, the amount of sample left after 120 years is 21.9 grams