Question 1156281
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..., make 50 ml of an alcohol solution with a 12% concentration. He has a 10% alcohol solution and a 15% alcohol solution.
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If want x of the 10% alcohol, then use 50-x of the 15% alcohol.


Accounting for quantities of alcohol to give the expected amount of pure alcohol:    {{{0.10x+0.15(50-x)=0.12*50}}};


{{{0.1x+0.15*50-0.15x=0.12*50}}}

{{{(0.1-0.15)x=0.12*50-0.15*50}}}

{{{(0.15-0.1)x=0.15*50-0.12*50}}}

{{{highlight(x=50((0.15-0.12)/(0.15-0.1)))}}}, and you can finish this.