Walking at $\dfrac{3}{4}$ of his usual speed, a man reaches school $20$ minutes late. His usual time (in…

Walking at $\dfrac{3}{4}$ of his usual speed, a man reaches school $20$ minutes late. His usual time (in minutes) is:
  1. $45$
  2. $50$
  3. $60$
  4. $80$

Solution

New time $= \dfrac{4}{3} \times $ usual. Extra $= \dfrac{1}{3} \times $ usual $= 20$, so usual $= 60$ min.

Asked in: IMO

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