\(\displaystyle{\chi_{{{1}-{0.05}}}^{{2}}}={\chi_{{{0.95}}}^{{2}}}={8.672}\)

\(\displaystyle{\chi_{{{0.05}}}^{{2}}}={27.587}\)

The boundaries of the confidence internal for the standart deviation are then:

\(\displaystyle\sqrt{{\frac{{{n}-{1}}}{{{\chi_{{\frac{\alpha}{{2}}}}^{{2}}}}}}}{s}=\sqrt{{\frac{{{18}-{1}}}{{{27.587}}}}}{35}\approx{27.475}\)

\(\displaystyle\sqrt{{\frac{{{n}-{1}}}{{{\chi_{{\frac{\alpha}{{2}}}}^{{2}}}}}}}{s}=\sqrt{{\frac{{{18}-{1}}}{{{8.762}}}}}{35}\approx{49.004}\) The boundaries of the confidence intervals for the stadart deviation:

\(\displaystyle{\left({27.475}^{{{2}}},{49.004}^{{{2}}}\right)}={\left({754.876},{2401.382}\right)}\)

Variance:(754.876,2401.392)

Standart deviation: (27.475,49.004)