SOLUTION: How many gallons of a 15% acid solution must be mixed with 5 gal of a 30% acid solution to make a 20% acid solution?

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Question 1102918: How many gallons of a 15% acid solution must be mixed with 5 gal of a 30% acid solution to make a 20% acid solution?
Found 2 solutions by josgarithmetic, greenestamps:
Answer by josgarithmetic(39623) About Me  (Show Source):
You can put this solution on YOUR website!
x gallons of 15% acid

15x%2B30%2A5=20%28x%2B5%29-------If this makes sense for you, then just continue to solve.

Answer by greenestamps(13203) About Me  (Show Source):
You can put this solution on YOUR website!


The other tutor showed how to set up the problem using the standard algebraic method for solving "mixture" problems.

Here is a quick solution using a different method....

(1) The desired percentage, 20%, is "twice as close" to 15% as it is to 30%.
(2) That means the mixture must use twice as much of the 15% ingredient as the 30% ingredient.
(3) Since the problem says there are 5 gallons of the 30% ingredient, you need 10 gallons of the 15% ingredient.