A photograph $4\,\text{cm} \times 6\,\text{cm}$ is enlarged so that its longer side becomes $15\,\text{cm}$.…

A photograph $4\,\text{cm} \times 6\,\text{cm}$ is enlarged so that its longer side becomes $15\,\text{cm}$. What is the new shorter side (in cm)?
  1. $8$
  2. $9$
  3. $10$
  4. $12$

Solution

Sides scale by the same factor: $\dfrac{15}{6} = 2.5$. New shorter side $= 4 \times 2.5 = 10$ cm.

Asked in: IMO

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