Combined meanmediumFree question
Combined mean Numerical Reasoning Question
| Group | Size | Mean |
|---|---|---|
| A | 8 | 40 |
| B | 9 | 86 |
Two groups are combined. What is the mean of the combined group?
A61.60
B126
C86
D64.40
E63.0
Worked solution
Combined mean = (n₁ × mean₁ + n₂ × mean₂) ÷ (n₁ + n₂) — weight by group size, never average the two means. The correct answer is 64.40. Traps to avoid: 61.60 comes from the "swapped weights" error; 126 comes from the "summed means" error; 86 comes from the "took larger group mean" error; 63.0 comes from the "unweighted mean" error.
The wrong answers here have names
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