Question 1207820
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First, a standard formal algebraic solution....<br>
You are mixing 60cc of 40% acid with x cc of 15% acid to obtain (60+x) cc of 25% acid:<br>
{{{.40(60)+.15(x)=.25(60+x)}}}<br>
Perhaps multiply by 100 to get rid of the decimals....<br>
{{{2400+15x=1500+25x}}}
{{{900=10x}}}
{{{x=90}}}<br>
ANSWER: 90cc<br>
Next, a solution by an informal method that can be used to solve any 2-part mixture problem like this....<br>
Look at the three percentages 15, 25, and 40 (on a number line, if it helps) and observe/calculate that 25 is 10/25 = 2/5 of the way from 15 to 40.<br>
That means 2/5 of the mixture is the higher percentage acid -- i.e., the mixture is 2 parts 40% acid and 3 parts 15% acid.<br>
Use a proportion to find that, since 2 parts of the mixture is 60cc, 3 parts of the mixture is 90cc.<br>
ANSWER (again, of course): 90 cc<br>