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What would be the correct mean, if the mean of 100 items was found to be 64 and later on it was discovered that two items were misread as 26 and 9 instead of 36 and 90 respectively?

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65.80

64.81

67.81

66.81

answer is B.

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Detailed Solution

We have to find the correct mean, if the mean of 100 items was found to be 64 and later on it was discovered that two items were misread as 26 and 9 instead of 36 and 90 respectively.
We know that,

mean = sum of all observations total number of observations

We have the mean as 64.

Sum of items 100 = 64 Sum of items = 64 × 100 = 6400

According to the question, calculating the new mean as,

6400 + 81 = 6481

Hence, the new mean is,

6481100 = 64.81

Thus, the new mean is 64.81.
Therefore, option 2 is correct.

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