A depletion type $N$-channel MOSFET is biased in its linear region for use as a voltage controlled resistor. Assume threshold voltage $V_{TH} = -0.5\:V,V_{GS} = 2.0\:V,V_{DS} = 5\:V,\:W/L = 100,C_{ox} = 10^{-8}\:F/cm^{2}$ and $\mu_{n} = 800\:cm^{2}/V$-$s.$ The value of the resistance of the voltage controlled resistor $(\text{in}\: \Omega)$ is _______.