Answer:
5 gallons of 50 % alcohol solution is used
Solution:
Let "x" is the gallons of 50 % alcohol solution
Then, 10 gallons is 35 % solution
The, 10 + x is the gallons of 40 % solution
Then, according to question,
"x" gallons of 50 % solution is mixed with 10 gallons of 35 % solution to get 10 + x gallons of 40 % solution
Therefore,
Thus 5 gallons of 50 % alcohol solution is used
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