Posted by **Vicki** on Thursday, February 16, 2012 at 1:16pm.

In what proportion should 95% alcohol be mixed with 30% alcohol to make 70% alcohol?

- MATH HELP -
**MathMate**, Thursday, February 16, 2012 at 2:37pm
0.......30%......70%......95%......100

.............40.......25..............

Look at the proportions above,

between 70% and 30%, the difference is 40%

and between 95% and 70%, the difference is 25%.

They should be mixed in the inverse ratio, i.e.

25 parts of 30% to 40 parts of 95%.

Converted to ratios,

25/(25+40)=25/65=5/13

40/(25+40)=40/65=9/13

So we mix (5/13) parts of 30% with (8/13) parts of 95% alcohol.

You can also solve it with algebra:

Let x be the fraction of 30% alcohol, then

30%*x+95%*(1-x) = 70%

Solve for x to get 5/13

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