Weighted Average
Section: Statistics & ProbabilityBank code: STA-WAVGRE frequency: HighPro
1. Core Idea
When groups have different sizes, you cannot average their averages. Each group's average must be weighted by how many members it has.
Weighted average = (sum of all values) / (total count) = (n1 x a1 + n2 x a2) / (n1 + n2)
The intuition worth teaching: the combined average is always pulled toward the larger group.
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