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A 75% alcohol concentration mixture of water and alcohol was made by mixing 30ml of pure alcohol with 150 ml of original mixture of water and alcohol. what was the alcohol concentration of the orignal mixture

The amount of water has not changed.

Since the final solution is 180 ml and is 75% alcohol, 25% or 45 ml must be water.

So that 45 ml of water must have been in the original 150 ml of the mixture which means 105 ml must have been alcohol

then the alcohol concentration of the original mixture was 105/150 or 70%

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