waecmaths question:
If $x\text{ }km{{h}^{-1}}=y\text{ }m{{s}^{-1}}$ then y =
Option A:
$\tfrac{7}{18}x$
Option B:
$\tfrac{11}{20}x$
Option C:
$\tfrac{4}{15}x$
Option D:
$\tfrac{5}{18}x$
waecmaths solution:
$\begin{align} & x\text{ }km{{h}^{-1}}=y\text{ }m{{s}^{-1}} \\ & 1000m=1km \\ & 3600s=1h \\ & \frac{x\times 1000}{3600}=\frac{5x}{18}m{{s}^{-1}} \\ & \frac{5x}{18}m{{s}^{-1}}=ym{{s}^{-1}} \\ & y=\frac{5x}{18} \\\end{align}$
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