Geometric Probability - Coin on Tiled Floor

For a coin of radius $r = 3\text{ cm}$ to lie completely inside a $10\text{ cm} \times 10\text{ cm}$ tile, its center must be at least $3\text{ cm}$ away from each side. The allowable region for the center is a square of side $10 - 2(3) = 4\text{ cm}$. Probability = $\frac{\text{Area of inner square}}{\text{Area of tile}} = \frac{4^2}{10^2} = \frac{16}{100} = 0.16$.