A single number can describe a whole data set, and a second number can say how far to trust the first. This unit follows that path: put the data in order as a stem-and-leaf plot and read the mode and the median, share the total out equally to find the mean, see what one extreme value does to each of the three, and then measure how spread out the data is with the range, the quartiles and the interquartile range. It finishes with box plots, which draw all of that on one line so that two groups can be compared fairly.
Every idea is something you can move: place waiting times one at a time, slide a level up six bars until it balances, drag one journey to an extreme, halve four small data sets, and build a box plot step by step before comparing two villages on one axis. No calculator is needed anywhere in this unit.
The lessons, in order
- Lesson 1 · Stem-and-leaf plots, mode and median Stem-and-leaf plots with a key (including back-to-back), the mode and the median of a list or a plot. Place 21 waiting times one at a time, put the leaves in order, and watch the mode and the median settle. No calculator
- Lesson 2 · The mean as a fair share The mean from a list and from a frequency table, the mean as a balance point, and finding a missing value from a mean. Slide a level up six bars until the books above it fill the gaps below it, and read off the mean. No calculator
- Lesson 3 · Outliers and choosing an average What an outlier is, how it affects the mean, median and mode, and choosing the most appropriate average for a context. Slide one bus journey from 18 to 90 minutes and see which of the three averages follows it. No calculator
- Lesson 4 · Range, quartiles and the interquartile range The range, the median, the lower and upper quartiles, the interquartile range and the five-number summary of a list of values. Split four small data sets into halves and read the quartiles, the range and the IQR from the same dots. No calculator
- Lesson 5 · Box plots and comparing data Drawing and reading box-and-whisker plots, and comparing two data sets on the same axis by median, interquartile range and range. Build a box plot from nine values in four steps, then compare two villages' water-fetching times on one axis. No calculator
Every lesson has a teacher page with the answers, the misconceptions each wrong answer reveals, discussion questions, differentiation and support for students learning in English, and extra questions in three tiers.