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 \(250 - 3x\)
waec 2017furthermathematics

The correct answer is B. \(225 - \frac{3x}{2}\)

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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