SOLUTION: How many gallons of a 7% salt solution must be mixed with 20 gallons of a 13% solution to obtain a 10% solution

Question 1181853: How many gallons of a 7% salt solution must be mixed with 20 gallons of a 13% solution to obtain a 10% solution
Found 3 solutions by josgarithmetic, greenestamps, MathTherapy:
Answer by josgarithmetic(39617)   (Show Source): You can put this solution on YOUR website!
How many gallons of 7%, g.

-

-------now just compute this.

~~g look s like 15 gallons.~~
The arithmetic should be simple from there.

Answer by greenestamps(13200)   (Show Source): You can put this solution on YOUR website!

10% is exactly halfway between 7% and 13%, so the two ingredients must be mixed in equal amounts.

ANSWER: 20 gallons

The method shown by the other tutor for solving the problem is valid... but their bad arithmetic at the end resulted in a wrong answer.

Answer by MathTherapy(10552)   (Show Source): You can put this solution on YOUR website!
How many gallons of a 7% salt solution must be mixed with 20 gallons of a 13% solution to obtain a 10% solution
g look s like 15 gallons. <=== The ANSWER is NOT 15 gallons.

ERROR again, from one of the MANY error-prone "responders/respondents" in this forum.
The 7%'s volume is being increased by 3% to 10%, while the 13%'s volume is being reduced by 3% to 10%.
With 1 volume being increased and the other decreased by the same amount, the different concentrations to be mixed will be the same.
Therefore, CORRECT ANSWER:
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