① Median and quartilesNo calculator
Split the ordered numbers into two halves. The median of each half gives the lower and upper quartile.
② Range and interquartile rangeNo calculator
Range = largest − smallest. Interquartile range = upper quartile − lower quartile.
③ Reading a box plotNo calculator
The box runs from the lower quartile to the upper quartile, with the median marked inside it.
④ Comparing box plotsNo calculator
Compare the medians (averages) and the interquartile ranges (spread).
⑤ Drawing a box plotNo calculator
Draw a scale, then the box, the median line and the two whiskers.
⑥ Is the box plot correct?No calculator
Work out the five-number summary from the data, then check each part of the box plot against it.
Key steps
Quartiles: put the numbers in order, find the median, then find the median of the lower half (lower quartile) and of the upper half (upper quartile). With an odd number of values, leave out the median.
Interquartile range = upper quartile − lower quartile.
Box plot: whiskers go to the minimum and maximum, the box goes from the lower to the upper quartile, and the line inside is the median.
Comparing: a higher median means a higher average; a smaller interquartile range means more consistent data.