Multiple choice

Alcohol is mixed with water in the ratio 5 : 2. If the mixture is 7 litres, how many litres of the mixture must be replaced with water to make the ratio of alcohol to water 1 : 1?

  1. 1.8 litres

  2. 2.1 litres

  3. 3.4 litres

  4. 1.6 litres

  5. 2.4 litres
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The initial 7-litre mixture contains 5 litres of alcohol and 2 litres of water. If x litres of the mixture is replaced by water, the remaining alcohol is 5 - (5/7)x and the new water content is 2 - (2/7)x + x. Setting these equal for a 1:1 ratio gives 5 - (5/7)x = 2 + (5/7)x, which solves to x = 2.1 litres.

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