SOLUTION: How much water should be mixed with an 8% plant fertilizer solution to make a half gallon of a 2% plant fertilizer solution? ______ gallons of water should be mixed with an 8%

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Question 1126707: How much water should be mixed with an 8% plant fertilizer solution to make a half gallon of a 2% plant fertilizer solution?
______ gallons of water should be mixed with an 8% plant fertilizer solution to make a half gallon of a 2% plant fertilizer solution.
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
From 8% to 2% is cutting the concentration to 1%2F4.
Three parts of the 8% to one part of the water.

Half-gallon is 4 pints.

Use 3 pints of the 8% and 1 pint of water.

Answer by ikleyn(52790) About Me  (Show Source):
You can put this solution on YOUR website!
.

            The solution by  @josgarithmetic  is   T O T A L L Y   W R O N G.

            Below find a correct solution. 


Let x be the volume of water to be added, in gallons.

Then the volume of the 8% plant fertilizer solution to use is (0.5-x) gallons.


The 8% plant fertilizer solution contains 0.08*(0.5-x) gallons of the pure fertilizer.


Divided by the total volume of 0.5 gallons, it should give the 2% concentration


    %280.08%2A%280.5-x%29%29%2F0.5 = 0.02.


Simplify by multiplying both sides by 0.5


    0.08*(0.5-x) = 0.5*0.02 = 0.01.


It gives you


    0.5 - x = 0.01%2F0.08 = 1%2F8,   and then


    x = 0.5 - 1%2F8 = 3%2F8 gallons of water.    


Answer.  3%2F8 gallons of water should be added, which is exactly 3 pints of water.

Solved.

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Compare it with the answer by @josgaritmetic, who gives 1 pint of water.


@josgarithmetic is VERY well known (or better to say, very badly known, unfortunately) in this forum,
for his inability to solve problems and make calculations correctly.


So be very careful when you obtain "solutions" from him.

In half of all cases they are wrong.

Do not trust him and always wait for reaction of other tutors.


In the normal school environment he would be fired in the second day.