Statistics & Averages
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Lesson overview
Mean, median and mode for grouped data.
Go to lesson quiz →Exam guidance · WAEC WASSCE Paper 1 + Paper 2 Lens
Core idea (Descriptive Statistics, Probability & Data Interpretation): Separate mutually exclusive events (add: P(A)+P(B)) from independent events (multiply: P(A)×P(B)), and check whether order matters (nPr vs nCr).
Pacing
Objective speed on Paper 1 + structured step-by-step method marks on Paper 2 Theory/Practical.
How WAEC marks this
Examiners award method marks (M1) for stating the formula/definition and accuracy marks (A1) ONLY when SI units are written.
Watch out for
Writing bare numbers without working or omitting SI units loses up to 50% of Paper 2 marks even when the final value is right.
Lesson content
Overview — Statistics & Averages
Mean, median and mode for grouped data. This lesson is at the advanced level — by the end, you'll be able to recognise this question type, apply a reliable method, and avoid the traps that cost marks.
Key Concept
Mean = sum of all values ÷ number of values. Median = the middle value when data is sorted in order (average the two middle values if there's an even count). Mode = the value that appears most often.
Why It's Tested This Way
Mean, median and mode are tested together because each answers a different question about the SAME data set, and WAEC wants candidates who know exactly which measure a question is actually asking for.
Method
Always SORT the data first when finding the median — the middle position only means something once the values are in order.
Worked Example
Worked example: For the numbers 3, 7, 5, 9: sorted = 3, 5, 7, 9; median = (5 + 7) ÷ 2 = 6. Mean = (3+7+5+9) ÷ 4 = 6.
Second Worked Example
Second worked example: For the numbers 2, 4, 4, 6, 9 (already sorted): median = 4 (the middle value); mode = 4 (appears twice); mean = (2+4+4+6+9) ÷ 5 = 5.
Common Traps
Common trap: finding the median without sorting the data first, or confusing mean (the average) with mode (the most frequent value) — they answer different questions about the same data.
Lesson Summary
Remember: (1) identify what is being asked, (2) apply the WAEC strategy, (3) check against the traps. Complete the 10-question quiz below to unlock the next lesson — you need at least 60% to pass.
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