1. The problem statement, all variables and given/known data Question Anna is calculating the mean and standard deviation for a set of data for a random variable X. The data is summarised in the table below. x: 10– 20– 30– 40–50 Frequency: 8 20 12 0 (i) For each of the following cases, write down the appropriate mid-values of the four intervals. (a) X is the weight of a letter, in grams. (This one is okay, variable is continuous) (b) X is the number of misprints in a magazine. (This one is okay, variable discrete) (c) X is the age, in complete years, of the audience at a cinema. (Problem) Answers: (a) 15, 25, 35, 45 (b) 14.5, 24.5, 34.5, 45 (c) 15, 25, 35, 45.5 (3 s.f.) 2. Relevant equations 3. The attempt at a solution I understand a) and b) fine. However, I can't figure out c) since I can't figure out what type of variable it is. I initially thought it would be discrete, due to the number of *complete* years. Would that not make the answer the same as that to b) though? Any clarification is greatly appreciated, exams coming soon :).