A fair six-sided die will be rolled twenty times, and the numbers that land face up will be recorded. Let z represent the average of the numbers that land face up for the first eight rolls, and the represent the average of the numbers landing face up for the remaining twelve rolls. The mean and variance o of a single roll are 2.92 and 3.5 respectively. What is the standard deviation (2) of the sampling distribution of the difference in sample means 21- x2? O3.523.52 3.5 +3.52 8 12 O 2.92+2.92 O3.5+ 3.5 3.5 3.5 + 12