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Grades 8–11 · CAPS · Gr 11 Term 4 - Statistics

Grade 11 Statistics

Ogives, variance and standard deviation, the shape of a distribution, and spotting outliers.

Gr 11 Term 4 - StatisticsTerm 4 - 3 weeks (CAPS)

Practise Statistics in the app →

What gets asked

Draw or read an ogive and take the median and quartiles from it.
Calculate the variance and standard deviation of ungrouped data.
Say whether data is symmetric or skewed, and in which direction.
Identify outliers and comment on them in context.

You must be able to

An ogive climbs through cumulative counts: read positions on the count axis first.
Standard deviation is the square root of the mean of the squared deviations.
Mean above median suggests a right skew; the box plot tells the same story.
Fences at 1,5 IQR beyond the quartiles mark off the outliers.

Traps that cost marks

Reading the median from the data axis instead of the halfway count. Find n over 2 on the cumulative axis, then trace across and down.
Averaging the deviations without squaring them. Plain deviations cancel to zero - square first, average, then root.
Calling the maximum an outlier automatically. Test it against the upper fence; a large value can still be ordinary.

Worked example

Find the standard deviation of

2; 4; 4; 6

.

Mean $= 4$ . Deviations: $- 2; 0; 0; 2$ .
Squares: $4; 0; 0; 4$ ; mean of squares $= 2$ .
$σ = 2 \approx 1, 41$ .

About this material

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