Help with my STATISTIC homework please!!?

The height of the 10 male students in a statistics cl are approximately normal with mean 70 inches and standard deviation 3 inches. The heights of the 10 females students in the same cl are also approximately normal with mean 65 inches and standard deviation 3 inches. Would the standard deviation for the height of all the students in the cl (men and women) be more than 3 inches, equal to 3 inches or less than 3 inches? explain.