Combined meanmediumFree question
Combined mean: Groups of 4 and 7
| Group | Size | Mean | Headcount |
|---|---|---|---|
| A | 4 | 41 | 1,377 |
| B | 7 | 64 | 2,406 |
Two groups are combined. What is the mean of the combined group?
Show worked solution
Combined mean = (n₁ × mean₁ + n₂ × mean₂) ÷ (n₁ + n₂) — weight by group size, never average the two means. The correct answer is 55.60. Traps to avoid: 49.40 comes from the "swapped weights" error; 105 comes from the "summed means" error; 64 comes from the "took larger group mean" error; 52.50 comes from the "unweighted mean" error.
The wrong answers here have names
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