When all the resistors are connected in series, the total resistance is

$R_{max}=10R$

$\Rightarrow R_{\max }=10\times 10=100 \mathrm{\Omega }$

When all the resistors are connected in parallel, the total resistance is

 $R_{min}=\frac{R}{10}$

$\Rightarrow R_{\min }=\frac{10}{10}=1 \mathrm{\Omega }$

Hence, the ratio,

 $\frac{R_{max}}{R_{min}}=\frac{100 \mathrm{\Omega }}{1 \mathrm{\Omega }}=100$.