Multiple choice

How much water (in litres) should be added to a 7.5-litre mixture of acid and water with acid-to-water ratio as 1 : 2, such that the resultant mixture has 20% acid in it?

  1. 10

  2. 2.5

  3. 7.5

  4. 5
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Initial: 7.5L, 1:2 ratio means 2.5L acid, 5L water. Let x be water added. New total = 7.5 + x. Acid remains 2.5L. We need 2.5 / (7.5 + x) = 0.20. 2.5 = 0.2(7.5 + x) = 1.5 + 0.2x. 1 = 0.2x, so x = 5.

AI explanation

In the initial 7.5-litre mixture with an acid-to-water ratio of 1 : 2, the acid quantity is 1/3 of 7.5, which equals 2.5 litres. For this 2.5 litres of acid to constitute 20% (or 1/5) of the new total volume, the total volume must be 2.5 multiplied by 5, resulting in 12.5 litres. Therefore, you must add 12.5 minus 7.5, which is 5 litres of water. The required amount of water is 5 litres.

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