Two groups of 10 and 15 observations have means 17 and 18 respectively. The combined mean of all 25 observations is:
Step-by-Step Solution
Key Concept: Use the combined-mean formula $\bar{x} = \frac{n_1\bar{x}_1 + n_2\bar{x}_2}{n_1 + n_2}$, which weights each group's mean by the number of observations it contains.
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Correct Answer: (2)