For Exercises 9–14, the frequency distribution is provided for a particular variable. Do the following:

  1. Find the class midpoints.
  2. Calculate the product of each class frequency with its midpoint.
  3. Find the sum of the frequencies, , and the sum of the products .
  4. Divide by to find the estimated mean of the variable, .

Question 3.224

11.

Class Frequency
10
20
30
20
10

3.3.11

(a)–(c)

Class Frequency Midpoint Product ·
10 1 10
20 3 60
30 5 150
20 7 140
10 9 90
Total

(d)