The radioactivity of given sample of whisky due to tritium (Half life=12 yrs) was found to be only 3.125% of that measured in a recently purchased bottle marked "10 years old". By how many years ago the sample must have been prepared?

Explanation

To solve the problem, we need to determine how many years ago the whisky sample was prepared based on its radioactivity due to tritium. Here’s a step-by-step solution:

### Step 1: Understand the given data
- The half-life of tritium (\( t_{1/2} \)) = 12 years.
- The radioactivity of the sample is 3.125% of that of a 10-year-old whisky bottle.

### Step 2: Express the radioactivity ratio
We can express the ratio of the radioactivities as:
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