Multiple choice

Mean of $9$ observations was founded to be $35$. Later on, it was detected that an observation $81$ was misread as $18$, then the correct mean of the observations is ____________.

  1. $40$
  2. $41$
  3. $42$
  4. $43$
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C Correct answer
Explanation

The sum of 9 observations was 9 * 35 = 315. The error was reading 18 instead of 81, a difference of 81 - 18 = 63. The correct sum is 315 + 63 = 378. The correct mean is 378 / 9 = 42.

AI explanation

The incorrect sum of the 9 observations is 9 multiplied by 35, which equals 315. The correct sum is found by subtracting the incorrect observation and adding the actual value, giving 315 minus 18 plus 81, which equals 378. Dividing this correct sum by 9 yields 42. The correct mean is 42.

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