The average of 30 values was calculated as 42. It was then found that one value had been taken as 71 by mistake. With the correct value in place, the average is 41.2. What is the correct value?

47Correct answerYour answer70.2Correct answerYour answer71.8Correct answerYour answer95Correct answerYour answer

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CorrectNot quiteAnswer A

Correct answer: A

The average dropped by $42 - 41.2 = 0.8$ , so the total dropped by $30 \times 0.8 = 24$ .
The wrong entry was 24 too high.
Correct value = $71 - 24 = 47$ .

Worth noting

The 0.8 is per value; the change in the one entry is $30 \times 0.8$ . 95 adds the 24 instead of subtracting it.

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