Open Class Interval Problem from AS S1

[Micky76]

Homework Statement

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.)

Homework Equations

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 :).

 

[Micky76]

Problem solved.