SOLUTION: To conduct a new experiment, a scientist needs a 20% salt water solution. How much of a 7.5% solution must be mixed with 40 quarts of a 25% solution to get the proper solution?

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Question 352253: To conduct a new experiment, a scientist needs a 20% salt water solution. How much of a 7.5% solution must be mixed with 40 quarts of a 25% solution to get the proper solution?
Found 2 solutions by Fombitz, ewatrrr:
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Let A be the amount of 7.5% solution.
Concentration equation:
7.5%28A%29%2B25%2840%29=20%28A%2B40%29
7.5A%2B1000=20A%2B800
12.5A=200
highlight%28A=16%29quarts

Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
Hi,
*Note: Let x be the "total amount of the 25% solution to be added
.
.075*x + .25*40qt = .20*(40qt + x)
.
.075*x + .25*40qt = 8qt + .20x
.
.075*x + 10qt -8qt = .20x
2qt = .125x
x = 16qt (the amount of the 7.5% solution needed to be added)
.
check your answer
.075*16 = 1.2qt of acid
.25 * 40qt = 10 qt of acid
1.2qt + 10qt = 11.2qt of acid in the final solution
.20* 56qt = 11.2 qt of acid