SOLUTION: How many liters of distilled water must be added to 140 liters of an 80 percent alcohol solution to obtain a 70 percent solution?

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Question 428537: How many liters of distilled water must be added to 140 liters of an 80 percent alcohol solution to obtain a 70 percent solution?
Found 3 solutions by mananth, ikleyn, josgarithmetic:
Answer by mananth(16949) About Me  (Show Source):
You can put this solution on YOUR website!
------ Percent ----------------quantity
Alcohol 80----------------140
water 0----------------x
Total 70----------------140+x
80*140 +0*x=70(140+x)
11200=9800+70x
-70x=9800-11200
-70x=-1400
/-70
x=20 gallons water

Answer by ikleyn(53418) About Me  (Show Source):
You can put this solution on YOUR website!
.

The correct answer is 20 liters - - - not 20 gallons.



Answer by josgarithmetic(39701) About Me  (Show Source):
You can put this solution on YOUR website!
Starts as 0.8%28140%29 liters of pure alcohol.

Add x liters of distilled water to make 70% alcohol.
%280.8%2A140%29%2F%28x%2B140%29=0.7

Simple algebra.
0.8%2A140=0.7x%2B0.7%2A140
0.8%2A140-0.7%2A140=0.7x
0.1%2A140=0.7x
x=%280.1%2A140%29%2F0.7
x=140%2F7
highlight%28x=20%29