a sample of 20 heads of lettuce was selected. assume that the population distribution of head weight is normal. the weight of each head of lettuce was then recorded. the mean weight was 2.2 pounds with a standard deviation of 0.1 pounds. the population standard deviation is known to be 0.2 pounds. in words, define the random variable x. x is the mean weight in pounds of a sample of 20 heads of lettuce. x is the population standard deviation of all heads of lettuce. x is the standard deviation of a sample of 20 heads of lettuce. x is the weight in pounds of a head of lettuce. x is the standard deviation of a sample of 20 heads of lettuce divided by the square root of 20. incorrect: your answer is incorrect.