smc

The answer we are looking for can be expressed as $\frac{100a+10b+c}{a+b+c}$. This is equivalent to $1+\frac{99a+9b}{a+b+c}$. Because we are trying to minimize our solution, we set $c$ = $9$, so we have $1+\frac{99a+9b}{a+b+9}$. This is equal to $1+\frac{9a+9b+81}{a+b+9}+\frac{90a-81}{a+b+9}$, which simplifies to $10+\frac{90a-81}{a+b+9}$. Since each digit is unique, we set $b$ to $8$, leaving us with $10+\frac{90a-81}{a+17}$. Clearly, $a$ should be minimized, so $a=1$ and our answer is $$\boxed{10.5}.$$