Answer 1)

Initial amount of the solution = 12 quarts

Amount of mango in juice is 20% of 12 quarts = 2.4 quarts

And mango concentrate is 15% of Y ml solution, where Y is new total of mango concentrate and water, after water being added to the solution.

So,

Y * 15% = 2.4 [Since, the amount of mango concentrate remains same]

=> Y = 2.4 * 100 / 15 = 16

So the amount of water added is New Amount - Old Amount = 16 -12 =4 quarts

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Answer 2)

Initial amount of the solution = 40 litres

Amount of alcohol in solution is 65% of 40 litres = 26 litres

So, the amount of water = 40 -26 = 14 litres

And water is 20% of Y ml solution, where Y is new total of alcohol and water, after alcohol being added to the solution.

So,

Y * 20% = 14 [Since, the amount of water remains same]

=> Y = 14 * 100 / 20 = 70

So the amount of alcohol added is New Amount - Old Amount = 70 - 40 = 30 litres