In calculating the mean of 8 numbers, a boy mistakenly used 17 instead of 25 as one of the numbers. If he obtained 20 as the mean, find the correct mean.
Take Free Practice Test On 2026 JAMB UTME, Post UTME, WAEC SSCE, GCE, NECO SSCE
Correct Answer: Option C
Explanation:
Let the sum of the 8 numbers = y.
\(\frac{y}{8} = 20 \implies y = 20 \times 8 = 160\)
\(160 - 17 = 143 (\text{the sum of the other 7 numbers})\)
\(mean = \frac{143 + 25}{8} = \frac{168}{8}\)
= 21
Let the sum of the 8 numbers = y.
\(\frac{y}{8} = 20 \implies y = 20 \times 8 = 160\)
\(160 - 17 = 143 (\text{the sum of the other 7 numbers})\)
\(mean = \frac{143 + 25}{8} = \frac{168}{8}\)
= 21