A radioactive substance decays according to , with in years. If its half-life is 10 years, the value of is:
Answer and explanation
Correct answer: D.
- Step 1: After 10 years, , so .
- Step 2: Take natural logs: , so .
Answer
.
Why not the others: is the inverse of the answer; swaps the roles of 2 and 10; treats half-life as a drop to one fifth.
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