One of the hazards of nuclear explosion is the generation of `.^(90)Sr` and its subsequent incorporation in bones. This nuclide has a half-life of `28.1` year. Suppose one micro-gram was absorbed by a new-born child, how much `Sr^(90)` will remain in his bones after 20 year?

Explanation

To solve the problem of how much \( \text{Sr}^{90} \) will remain in the bones of a newborn child after 20 years, we can follow these steps:

### Step 1: Understand the Given Information
- Initial amount of \( \text{Sr}^{90} \) absorbed: \( 1 \, \mu g = 1 \times 10^{-6} \, g \)
- Half-life of \( \text{Sr}^{90} \): \( 28.1 \, \text{years} \)
- Time elapsed: \( 20 \, \text{years} \)

### Step 2: Calculate the Number of Half-Lives
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