A metal block has dimensions $10\text{cm}\times 5\text{cm}\times 2\text{cm}$ . The ratio of maximum to minimum resistance that can be obtained from it is

$\text{R}=\frac{\rho l}{\text{A}}$                                               

$\text{If},l_1=10\text{cm,}{\text{A}}_{\text{1}}=10{\text{cm}}^{\text{2}}$

${\text{R}}_1=\frac{\rho .10}{10}=\rho \text{Ohm}$

$\text{If,}{l}_1=2\text{cm,}{\text{A}}_{\text{2}}=50{\text{cm}}^{\text{2}}$

$R_2=\frac{\rho .2}{50}=\frac{\rho }{25}\text{ohm}$

$\text{If,}{l}_3=5\text{cm,}{\text{A}}_{\text{3}}=20{\text{cm}}^{\text{2}}$

$R_3=\frac{\rho l_3}{{\text{A}}_{\text{3}}}=\frac{\rho .5}{20}=\frac{\rho }{\text{4}}\text{ohm}$

$\therefore \frac{{\text{R}}_{\text{max}}}{{\text{R}}_{\text{min}}}=\frac{\rho }{\rho \text{/25}}=\frac{25}{1}$