Multiple choice

How much water must be added to $300$ litre of a solution so that its concentration may change from $25\%$ to $20\%$?

  1. $70$ litre.
  2. $75$ litre.
  3. $67$ litre.
  4. $98$ litre.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Initial solute = 25% of 300 = 75. Let x be water added. New concentration = 75 / (300 + x) = 20/100 = 1/5. 375 = 300 + x, so x = 75.

AI explanation

The initial amount of the solute in the solution is 25 percent of 300 litres, which is 75 litres. By adding x litres of water, the new total volume becomes 300 + x litres, so the new concentration is 75 / (300 + x) = 0.20. Solving this equation gives 75 = 60 + 0.20x, which means 0.20x = 15 and x = 75. The required amount of water to add is 75 litres.

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