If the price of sugar increases by $25\%$, by what percent must a family reduce its consumption so that…

If the price of sugar increases by $25\%$, by what percent must a family reduce its consumption so that expenditure on sugar is unchanged?
  1. $25\%$
  2. $20\%$
  3. $15\%$
  4. $10\%$

Solution

Required reduction $\% = \dfrac{r}{100 + r} \times 100 = \dfrac{25}{125} \times 100 = 20\%$. Verification: $1.25 \times 0.80 = 1$.

Asked in: IMO

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