In a class of 10 boys and 15 girls, the average score in a Biology
FURTHER MATHEMATICS
WAEC 2017
In a class of 10 boys and 15 girls, the average score in a Biology test is 90. If the average score for the girls is x, find the average score for the boys in terms of x.
- A. \(200 - \frac{2x}{3}\)
- B. \(225 - \frac{3x}{2}\)
- C. \(250 - 2x\)
- D. \(250 - 3x\)
Correct Answer: B. \(225 - \frac{3x}{2}\)
Explanation
Let A and B be the sum for the boys and girls respectively.
\(\frac{A + B}{10 + 15} = \frac{A + B}{25} = 90\)
\(\implies A + B = 90 \times 25 = 2250\)
Given the average for girls = x, we have \(\frac{B}{15} = x \implies B = 15x)
\(\therefore A + 15x = 2250; A = 2250 - 15x \implies\) average score for boys \(= \frac{2250 - 15x}{10}\)
= \(225 - \frac{3x}{2}\)
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