M4.7.2 For the adult
Averages from frequency tables
Mei opens 25 pea pods and counts the peas in each. How can she find the mean number of peas without adding 25 numbers?
What this chapter teaches
The mean from a frequency table is ∑fx ÷ ∑f. For grouped data the midpoint of each class stands for its values, so the answer is an estimate. The median is the (n + 1) ÷ 2 th value, and the running total of the frequencies shows its class.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why do we multiply each value by its frequency before we add?
- Why is a mean from grouped data an estimate, and how far could it be wrong?
- There are 25 values in order. Which one is the median, and how do you find its class from a table?
After the chapter, the learner can
- Find the mean from a frequency table
- Estimate the mean from grouped data
- Find the group that holds the median
What they copy into their notebook
Mean = ∑fx ÷ ∑f. For classes, use midpoints and say estimate. Median place = (n + 1) ÷ 2: add the frequencies until the running total reaches it.