Answer :
We need 65 ml of 50% mixture to obtain the desired solution.
Here, we need to make a 25% alcohol solution by mixing some amount of 50% alcohol mixture with 325 mL of a 20% alcohol mixture.
Let the amount of 50% alcohol solution be x
The the quantity of alcohol in 50% alcohol solution = 50% of x
= 0.5x
Similarly the the quantity of alcohol in 20% alcohol solution = 20% of 325
= 65ml
The total quantity of 25% alcohol solution = (325 + x) ml
Thus, the the quantity of alcohol in 25% alcohol solution = 25% of (325 + x)
= 0.25 (325 + x)
= 81.25 + 0.25x
Thus, we can form the following equation-
0.5x + 65 = 81.25 + 0.25x
0.5x - 0.25x = 81.25 - 65
0.25x = 16.25
x = 16.25/ 0.25
x = 65
Thus, we need 65 ml of 50% mixture to obtain the desired solution.
Learn more about weighted averages here-
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