Question 1128218
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Here is a quick way to solve mixture problems like this without the formal algebra.  If you understand this method, it will get you to the answer much faster than algebra.<br>
66 is 6 away from 72 and 24 away from 42.
The ratio of 6 and 24 is 6:24 or 1:4; that means the ingredients must be mixed in the ratio 4:1.
A ratio of 4:1 to make 10 liters means 8 liters of one and 2 liters of the other.
Since 66% is closer to 72% than to 42%, you need 8 liters of the 72% and 2 liters of the 42%.