Cumulative frequency and box-and-whisker plots
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 7 practice questions, 1 real past-paper question with the answer explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Five numbers tell the story
- Cumulative frequency
- Plotting the curve
Read the transcript of the teaching part
Last time
Before we start: last time, in Mean, median, mode and range, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Five numbers tell the story
Two classes took the same test. Each can be summarised by five numbers: smallest, lower quartile, median, upper quartile and largest. Draw them as a box with whiskers, and you can compare the classes at a glance. Cumulative frequency is how we get those five numbers from grouped data.
Cumulative frequency
Cumulative frequency is the running total of the frequencies. Sixty students, grouped by hours of television: six, fourteen, twenty, fourteen, six. Add as you go: six, twenty, forty, fifty-four, sixty. The last one equals the total. Always check that the last value is the total number of data points.
Plotting the curve
Plot each cumulative frequency at the upper end of its class: one hour, two hours, three, four, five. Start at zero, zero. Join the points with a smooth curve, rising in an S shape. Never use a ruler. Label the axes: the data on the horizontal axis, cumulative frequency on the vertical.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Reading a cumulative frequency curve.
The whole chapter: Cumulative Frequency and Histograms.
Chapter 32: Cumulative frequency and histograms
- Cumulative frequency and box-and-whisker plots 6 min
- Histograms 6 min
Also for O Level Maths 4024
Which topics come up most in O Level Maths 4024 past papers, counted from every paper since 2004.