Arandom sample of size n1 = 10 is selected from a normal population with a mean of 120 and a standard deviation of 12. a second random sample of size n2 = 15 is selected from a normal population with a mean of 105 and a standard deviation of 20. let m1 and m2 be the two sample means. the two populations are thought to be independent. let x = m1 – m2 find: (d) the expected value and the variance of x. (e) the probability that x exceeds 10. (f) the probability that x is between 12.5 and 17.5.