Grade 9 Data Handling

Grade 9 data handling: collecting and organising data, mean, median, mode and range, and choosing and reading graphs such as histograms and pie charts.

Data handling is about collecting, organising, summarising and representing information, then saying what it means. In Grade 9 you calculate the mean, median, mode and range, group data into intervals, and choose and draw suitable graphs.

You also learn to spot misleading graphs and to compare two sets of data. Grade 10 adds quartiles and box-and-whisker plots, and Grade 11 adds standard deviation, so understanding the basic measures now is important.

Key concepts

  • Mean = sum of values ÷ number of values
  • Median: the middle value of sorted data
  • Mode: the value that occurs most often
  • Range = largest value − smallest value
  • Bar graphs, histograms, pie charts, line graphs and scatter plots
  • Grouping data in class intervals and tallying

Worked examples

Find the range of 12; 7; 19; 3; 15.

Range = largest − smallest = 19 − 3 = 16.

Find the median of 8; 3; 10; 5; 6; 12.

Sort the data: 3; 5; 6; 8; 10; 12. There are two middle values, 6 and 8, so the median is (6 + 8) ÷ 2 = 7.

In a pie chart, 40 out of 160 learners chose soccer. What angle is the soccer sector?

40 ÷ 160 = ¼ of the learners, and ¼ of 360° = 90°.

Which graph best shows how a learner's marks changed over a year?

A line graph, because it shows change over time. A pie chart shows parts of a whole, not change.

The marks of five learners are 45; 60; 60; 72 and 88. Find the mean, median and mode.

Mean = (45 + 60 + 60 + 72 + 88) ÷ 5 = 325 ÷ 5 = 65. The median (middle value) is 60, and the mode (most common value) is also 60.

Common mistakes

  • Finding the median without sorting the data.
  • Leaving gaps between the bars of a histogram.
  • Pie chart angles that don't add up to 360°.
  • Saying the mode is how many times a value occurs, instead of the value itself.

Exam tips

  • Sort the data before you find the median.
  • Give every graph a title and label both axes.
  • When comparing data sets, mention both a measure of centre and the range.

Frequently asked questions

When is the median better than the mean?

When the data has outliers. For example, one very high salary pulls the mean up, but the median still shows a typical value.

What is the difference between a bar graph and a histogram?

A bar graph shows separate categories, with gaps between the bars. A histogram shows grouped numerical data, so the bars touch.

Can data have more than one mode?

Yes. If two values occur equally often and more than the rest, the data is bimodal. If every value occurs once, there is no mode.

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