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Question 141
The arithmetic mean of 100 observations is 10. Of these the arithmetic mean of the first 25 observations is 12 while that of the last 65 is 9. The arithmetic mean of the remaining 10 observationsis
Solution
Sum of all the 100 observations = 1000
Sum of the first 25 observations = 25*12 = 300
Sum of the last 65 observations = 65*9 = 585
Hence, the sum of the 10 observations between these 2 groups = 1000-300-585 = 115Â
Hence, the mean of these 10 observations = 115/10 = 11.5
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