A mixture of 0.1 mole of helium $\left(\gamma_1=C_p / C_v=5 / 3\right)$ with 0.2 mole of nitrogen $\left(\gamma_2=7 / 5\right)$, considered an ideal mixture of two ideal gases, is initially at 300 K and occupies 4 litres. Show that the changes of temperature and pressure of the system which occur when the gas is compressed slowly and adiabatically can be described in terms of some intermediate value of $\gamma$. Calculate the magnitude of these changes when the volume is reduced by $1 \%$.