As, γ is given, we can find f using following relation:
γ=1+2f
γ=117=1+47⇒f=72
The calculated f is for the mixture of gases, so f=fmixture
We know that, if two different types of gases are mixed at same temperature together, then the degree of freedom of the mixture is calculated by:
fmixture=n1.f1+n2.f2n1+n2
Here,
f1= Degree of freedom of gas 1=3
f2= Degree of freedom of gas 2=5
fmixture=72=n1.3+n2.5n1+n2⇒n1n2=3