The ph of a solution is measured eight times by one operator using the same instrument. she obtains the following data: 7.15, 7.20, 7.18, 7.19, 7.21, 7.20, 7.19, and 7.19. (a) calculate the sample mean. round your answer to 3 decimal places. entry field with correct answer 7.189 (b) calculate the sample variance. round your answer to 6 decimal places. entry field with incorrect answer .003 (c) calculate the sample standard deviation. round your answer to 3 decimal places. entry field with correct answer .018 (d) which of the following are potential major sources of variability in the experiment?