The mean of $4$ terms is $28$ if one observation $12$ is mistaken as $21$ Find the right mean

24.75

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25.75

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24.25

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25.25

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Solution

The correct option is B 25.75
No.of observations $4$
Mean of observation $28$
The sum of observations $28 \times 4 = 112$
The mistaken observation $21$
The sum of observation is $112 - 21 = 91$
The right observation is $12$
The sum of observations is $91 + 12 = 103$
The right mean is $\frac{103}{4} = 25.75$

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