If you start with 80 grams of cobalt-60, how many grams will remain after three half-lives?

• A. 10 grams
• B. 5 grams
• C. 40 grams
• D. 20 grams

Answer: (A)

Verified step by step guidance

1. Identify the initial amount of the substance, which is 80 grams of cobalt-60.
2. Recall the concept of a half-life: after one half-life, half of the original amount of the substance remains.
3. Use the formula for the remaining amount after n half-lives: \(\text{Remaining amount} = \text{Initial amount} \times \left(\frac{1}{2}\right)^n\).
4. Substitute the given values into the formula: \(\text{Remaining amount} = 80 \times \left(\frac{1}{2}\right)^3\).
5. Calculate the power of one-half raised to 3, then multiply by 80 to find the remaining grams after three half-lives.