So let me write that down. This is equal to 178 centimeters minus 170 centimeters, which is going to be equal to, I'll do it in this color, this is going to be equal to eight centimeters. So this is eight right over here. Now what about the standard deviation? Assuming these two random variables are independent, and they tell us that we are independently, randomly selecting a man and a woman, the height of the man shouldn't affect the height of the woman or vice versa. Assuming that these two are independent variables, if you take the sum or the difference of these, then the spread will increase. But you won't just add the standard deviations.