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In computing the mean of 8 numbers, a boy mistakenly used 17 instead of 25...

Further Mathematics
WAEC 2012

In computing the mean of 8 numbers, a boy mistakenly used 17 instead of 25 as one of the numbers and obtained 20 as the mean. Find the correct mean

  • A. 19
  • B. 21
  • C. 23
  • D. 24
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Correct Answer: Option B
Explanation

\(Mean = \frac{sum of items}{total number of items}\)

\(20 = \frac{x}{8} \implies x = 160\)

The sum of the 7 nos = 160 - 17 = 143

Correct mean = \(\frac{143 + 25}{8} = \frac{168}{8} = 21\)


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