Question 28

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Jambmaths question: 

y is inversely proportional to x and y = 4 when x = $\frac{1}{2}$. Find x when y =10

Option A: 

2

Option B: 

10

Option C: 

$\frac{1}{5}$

Option D: 

$\frac{1}{10}$

Jamb Maths Solution: 

$\begin{align}  & y\propto \frac{1}{x} \\ & y=\frac{k}{x} \\ & \text{when }x=\frac{1}{2},\text{ }y=4 \\ & 4=\frac{k}{{\scriptstyle{}^{1}\!\!\diagup\!\!{}_{2}\;}} \\ & k=4\times \frac{1}{2}=2 \\ & \text{when }y=10 \\ & 10=\frac{k}{x} \\ & x=\frac{2}{10}=\frac{1}{5} \\\end{align}$

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