Question 1111048
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Here is an alternative to the standard algebraic solution method that requires only a few simple calculations.<br>
(1) Find how far the desired 32% is from the 15% of the original solution and from the 100% of the pure alcohol.
100-32 = 68; 32-15 = 17<br>
(2) The ratio of the two numbers from (1) is the ratio in which the two ingredients must be mixed.
68:17 = 4:1<br>
Since the 32% is closer to 15% than to 100%, you need 4 parts of the original solution to 1 part of the added pure alcohol.  In other words, the amount of pure alcohol to be added should be 1/4 the amount of the original mixture.
1/4 of 800ml = 200ml<br>
Answer: He needs to add 200ml of pure alcohol.