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If x varies inversely as the cube root of y and x = 1 when...

Mathematics
JAMB 1988

If x varies inversely as the cube root of y and x = 1 when y = 8, find y when x = 3

  • A. \(\frac{1}{3}\)
  • B. \(\frac{2}{3}\)
  • C. \(\frac{8}{27}\)
  • D. \(\frac{4}{9}\)
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Correct Answer: Option C
Explanation

\(x \propto \frac{1}{\sqrt[3]{y}} \implies x = \frac{k}{\sqrt[3]{y}}\)

When y = 8, x = 1

\(1 = \frac{k}{\sqrt[3]{8}} \implies 1 = \frac{k}{2}\)

\(k = 2\)

\(\therefore x = \frac{2}{\sqrt[3]{y}}\)

When x = 3,

\(3 = \frac{2}{\sqrt[3]{y}} \implies \sqrt[3]{y} = \frac{2}{3}\)

\(y = (\frac{2}{3})^{3} = \frac{8}{27}\)


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