From the circuit shown below, the maximum and minimum values of zener diode current are

 $$\begin{gathered} \mathrm{maximum} \mathrm{voltage} \mathrm{across} 5 \mathrm{K\Omega } \mathrm{resistance} \mathrm{is} 70 \mathrm{V} \mathrm{and} \mathrm{constant} \mathrm{load} \mathrm{current} \mathrm{is} \frac{50}{10\times {10}^3}=5\mathrm{mA} \\ \mathrm{and} \mathrm{total} \mathrm{current} \frac{70}{5\times {10}^3}=14 \mathrm{mA} ; so \mathrm{maximum} \mathrm{Zenner} \mathrm{current} \mathrm{is} 9 \mathrm{mA} \\ \mathrm{similarly} \mathrm{mimimum} \mathrm{voltage} \mathrm{across} 5 \mathrm{K\Omega } \mathrm{resistance} \mathrm{is} 30 \mathrm{V} \\ \mathrm{and} \mathrm{minimum} \mathrm{current} \mathrm{is} \frac{30}{5\times {10}^{-3}}=6 \mathrm{mA} \mathrm{so} \mathrm{minimum} \mathrm{Zenner} \mathrm{current} \mathrm{is} 1 \mathrm{mA} \end{gathered}$$