ITPEC IP October 2018 Question 1
ITPEC IP October 2018 — Question 1 of 100
The overall average must be weighted by the number of students in each school. Each school's total pocket money is its student count multiplied by its average, so the combined average is (B2*C2+B3*C3+B4*C4)/SUM(B2:B4). This is exactly the formula in option (b).
Answer (b)
Why not others:
- averaging the three school averages gives every school equal weight despite different student counts
- dividing a total by the number of schools does not produce an average per student
- multiplying or summing the averages alone ignores the population represented by each value
Key rule: For groups of different sizes, use sum(group size * group average) / sum(group size).
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