One mole of an ideal monoatomic gas `(gamma = (5)/(3))` is mixed with one mole of a diatomic gas

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