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NDA 2017
Exam
NDA
Year
2017
Subject
Mathematics
Chapter
Statistics

NDA 2017 · Mathematics · Statistics

The mean of a group of 100 observations was found to be 20. Later...

The mean of a group of 100 observations was found to be 20. Later it was found that four observations were incorrect, which were recorded as 21,21,1821,21,18 and 20. What is the mean if the incorrect observations are omitted?

Options

  1. A18
  2. B20
  3. C21
  4. D22

Correct answer

B. 20

Step-by-step solution

 Mean of 100 observations =20Required mean =20×100−(21+21+18+20)96=192096=20\begin{aligned} & \text{ Mean of } 100 \text{ observations }=20 \\ & \text{Required mean }=\frac{20 \times 100-(21+21+18+20)}{96} \\ & =\frac{1920}{96}=20\end{aligned}
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