A car increases its speed by $25\%$. The time saved on a fixed journey (as a fraction of the original time)…

A car increases its speed by $25\%$. The time saved on a fixed journey (as a fraction of the original time) is:
  1. $\dfrac{1}{4}$
  2. $\dfrac{1}{5}$
  3. $\dfrac{1}{6}$
  4. $\dfrac{1}{3}$

Solution

New speed $= 1.25 \times $ old. New time $= \dfrac{\text{old}}{1.25} = \dfrac{4}{5}$ of old time. Time saved $= \dfrac{1}{5}$ of old time.

Asked in: IMO

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