ANSWER
The amount of sample left after 120 years is 21.9 grams
Step-by-step 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
![\text{ N = N}_o((1)/(2))^{(t)/(\iota)}](https://img.qammunity.org/2023/formulas/chemistry/college/e9mmufbuftbisdw5de64e04zcyzphcr8m6.png)
Step 2; Substitute the given data into the above formula
![\begin{gathered} \text{ N = 700 }*\text{ \lparen}(1)/(2))^{(120)/(24)} \\ \\ \text{ N = 700 }*\text{ \lparen}(1)/(2))^5 \\ \\ \text{ N = }\frac{700}{\text{ 32}} \\ \text{ N = 21.9 grams} \end{gathered}](https://img.qammunity.org/2023/formulas/chemistry/college/ta3f74ljtmrm593clykzrc8eetjurr5npa.png)
Therefore, the amount of sample left after 120 years is 21.9 grams