There are $11$ coins with $1$ unit radius and we are trying to put them inside a big disc with some radius. So
What is the minimum radius of this disc?
- If this question was asked for $2$ coins, the answer would be obviously $2$ unit radius,
- If was asked for $3$ coins, the answer would be $1+\frac{2}{\sqrt{3}}\cong 2.16$ unit radius as shown below: