Question 1126094
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Since this is a math website and not a chemistry website, we should allow the possibility that the given concentrations are unlikely or impossible.  The clear intention of the problem is to give you practice solving mixture problems.<br>
Here is the fastest way to solve such problems, without algebra.<br>
70% is 2/3 of the way from 50% to 80% (do a little mental arithmetic)
Therefore, 2/3 of the 1 liter mixture should be the 80% acid.<br>
(mathematical) ANSWER: 1/3 liter of 50% HCl and 2/3 liter of 80% HCl.