<PRE><B>Question 797963</B>
Let u = amount of 10% acid
Let v = amount of 20% acid


{{{(10u+20v)/2=18}}} and {{{u+v=2}}}
Solve for u and v.




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If you try the same or similar analysis for a target value of 18%, but using only the 10% and 15% acid solutions, you will obtain answers for u and v which do not make sense.</PRE>