Kinetic Theory of Gases Questions

Which one of the following statements is NOT true about the effect of an increase in temperature on the distribution of molecular speeds in a gas?

One mole of ideal monoatomic gas ($\gamma =5/3$) is mixed with one mole of diatomic gas ($\gamma =7/5$). What is $\gamma$ for the mixture? $\gamma$ denotes the ratio of specific heat at constant pressure to that at constant volume.