A man buys $11$ oranges for Rs. $10$ and sells $10$ oranges for Rs. $11$. His profit percent is

A man buys $11$ oranges for Rs. $10$ and sells $10$ oranges for Rs. $11$. His profit percent is
  1. $10\%$
  2. $11\%$
  3. $21\%$
  4. $22\%$

Solution

CP of $1$ orange $= \dfrac{10}{11}$; SP of $1$ orange $= \dfrac{11}{10}$. Profit $= \dfrac{11}{10} - \dfrac{10}{11} = \dfrac{121 - 100}{110} = \dfrac{21}{110}$. Profit\% $= \dfrac{21/110}{10/11} \times 100 = \dfrac{21}{110} \times \dfrac{11}{10} \times 100 = 21\%$.

Asked in: IMO

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