ISEE Mathematics Achievement Question 182: Answer and Explanation
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Question: 182
11. The half-life of a radioactive element is 1 second. If you start with 32 grams of it, how much will be left in 4 seconds?
- A. 2 g
- B. 4 g
- C. 8 g
- D. 16 g
Correct Answer: A
Explanation:
A is correct. If the element has a half–life of 1 second, one–half of its mass decays each second. If you start with 32 g, after 1 second, 
g are left. After 2 seconds, 
g are left. After 3 seconds, 
g are left. After 4 seconds, 
g are left.