Question 1163666
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You are mixing x ounces of 15% alcohol and 4 ounces of 20% alcohol to get (x+4) ounces of 17% alcohol:<br>
{{{.15(x)+.20(4) = .17(x+4)}}}<br>
Solve using basic algebra (I leave that to you).<br>
If a formal algebraic solution is not required, here is a quick informal solution method.<br>
You are starting with 20% alcohol and adding 15% alcohol; the more you add, the closer the mixture gets to 15%.<br>
You stop adding the 15% alcohol when the percentage of the mixture gets to 17%.<br>
17% is 3/5 of the way from 20% to 15%.  (If it helps, picture the three percentages 20, 17, and 15 on a number line.)<br>
That means 3/5 of the mixture is what you are adding.<br>
So the 4 ounces you started with is 2/5 of the mixture; that means 3/5 of the mixture is 6 ounces.<br>
So the amount of 15% alcohol you added is 6 ounces.<br>
ANSWER: 6 ounces of 15% alcohol should be used.<br>
Of course that is the answer you should get if you finish solving the problem by the algebraic method shown above.<br>