In a mixture of argon (atomic mass = 39.9 u) and neon (atomic mass = 20.2 u), the speed of sound is 363 m/s at 300K. Assume that both monatomic gases behave as ideal gases. Find the percentage of the atoms that are argon and the percentage that are neon. I found the solution (in the attachments) but what I can't figure out is where the equation that was used in step 4 of the solution came from. This is the equation that was used to solve the problem. Where did it come from? v = (v_{1}v_{2}(V_{1}+ V_{2})^{1/2})/(V_{2}v_{1}^{2} + V_{1}v_{2}^{2})^{1/2}