AC9M10ST04Year 10StatisticsPractised on site

AC9M10ST04 — Year 10 Statistics

Official Curriculum Content Description:

construct two-way tables and discuss possible relationship between categorical variables

Worked Examples (1)

Example 1Conditional Probability from Two-Way Tables

A survey of 66 students recorded their activity preferences. A student is chosen at random from those who prefer Netball. What is the probability that the student is a Boy? Express your answer as a fraction in its lowest terms.

Activity preferences

Group	Netball	Swimming	Total
Boys	18	18	36
Girls	18	12	30
Total	36	30	66

Common mistake: Using the grand total (66) as the denominator instead of the restricted sub-population total (36).

Correct Answer:

1/2

Worked Solution:

For conditional probability

P(B \mid A)

, restrict the denominator to the total students who prefer Netball (

36

) rather than the grand total (

66

). Numerator =

18

. Probability =

\frac{18}{36}

\frac{1}{2}

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