$A$ does $\dfrac{1}{4}$ of a work in $5$ days. The whole work will be done by $A$ in:

$A$ does $\dfrac{1}{4}$ of a work in $5$ days. The whole work will be done by $A$ in:
  1. $15$ days
  2. $18$ days
  3. $20$ days
  4. $25$ days

Solution

If $\dfrac{1}{4}$ takes $5$ days, full work takes $5 \times 4 = 20$ days.

Asked in: IMO

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