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Question
If the mean of 1, 2, 3, …, n is `(6"n")/11`, then the value of n is
Options
10
12
11
13
Solution
11
Explanation:
The mean of 1, 2, 3, …., n is `(6"n")/11`
i.e., `(1 + 2 + 3 + 4 + ... + "n")/"n" = (6"n")/11`
`(("n"("n" + 1))/2)/"n" = (6"n")/11`
`("n" + 1)/2 = (6"n")/11`
11 (n + 1) = 2 × 6n
11n + 11 = 12n
∴ n = 11
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