If $x \propto y$ and $x : y = 5 : 7$ for some pair, then for another pair with $y = 49$, the value of $x$ is:

If $x \propto y$ and $x : y = 5 : 7$ for some pair, then for another pair with $y = 49$, the value of $x$ is:
  1. $25$
  2. $30$
  3. $35$
  4. $70$

Solution

$\dfrac{x}{y} = \dfrac{5}{7}$, so $x = \dfrac{5}{7} \cdot 49 = 35$.

Asked in: IMO

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