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      Question

      A mixture contains 75% alcohol and rest water. A man

      withdrew some mixture using a cup and replaced it with same quantity of petrol, such that the quantity of alcohol remaining in the mixture now is 60%. If the man wants to bring down the quantity of alcohol to less than 40%, then how many more times should he repeat the same process?
      A 3 Correct Answer Incorrect Answer
      B 2 Correct Answer Incorrect Answer
      C 1 Correct Answer Incorrect Answer
      D 4 Correct Answer Incorrect Answer
      E Cannot be determined Correct Answer Incorrect Answer

      Solution

      Let the percentage of mixture withdrawn first time be β€˜p%’. ATQ; 75 Γ— {1 βˆ’ (p/100)} = 60 Or, 1 βˆ’ (p/100) = 0.8 Or, (p/100) = 0.2 So, p = 20 So, 20% mixture is drawn every time. Now, Quantity of alcohol remaining after withdrawing once more = 60 Γ— 0.8 = 48 And,
      Quantity of alcohol remaining after withdrawing once more = 48 Γ— 0.8 = 38.4 So, after withdrawing two more times, the quantity of alcohol reaches less than 40%.

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