Two gases A and B having the same pressure, P, volume V and temperature T are mixed. If the mixture has volume and temperature as V and T respectively the pressure of the mixture is

But P₁ = P₂ = P, V₁ = V₂ = V, T₁ = T₂ = T 
After mixing the two gases 
volume V¹ = V₁ = V₂ = V 
Temperature T¹ = T₁ = T₂ = T 
Pressure P¹ = ? 
no. of moles = n we have $\mathrm{n}=\frac{\mathrm{PV}}{\mathrm{RT}}$
But n = n₁ + n₂  $\frac{{\mathrm{P}}^1{\mathrm{V}}^1}{{\mathrm{RT}}^1}=\frac{\mathrm{PV}}{\mathrm{RT}}+\frac{\mathrm{PV}}{\mathrm{RT}}$
P¹ = 2P