Multiple choice

The mean of first 11 observations out of 12 is 95. The last observation is 33 more than the mean of all the observations. Calculate the last observation.

  1. 130

  2. 131

  3. 132.50

  4. 141.75
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B Correct answer
Explanation

Sum of 11 observations = 11 * 95 = 1045. Let total sum be S. S = 1045 + x, where x is the 12th observation. Mean = S/12 = (1045 + x)/12. Given x = (S/12) + 33. Substitute S: x = (1045 + x)/12 + 33. 12x = 1045 + x + 396. 11x = 1441. x = 131.

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