Question 1114594
x = 20% sugar solution
y = 100% (pure) sugar solution
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Make two equations.  The first equation is the total amount of solution.  The second equation is the total amount of sugar in the solution.

x + y = 2
0.20x + y = 0.25(2)
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Clean up the second equation:
x + y = 2
0.20x + y = 0.50
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Multiply the second equation by -1:
x + y = 2
-0.20x - y = -0.50
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Add the two equations together:
0.80x = 1.50
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Solve for x:
x = 1.875
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We now know the 20% solution (x) is 1.875 cups. Because x + y = 2...or, 1.875 + y = 2...that means the pure sugar solution (y) is 0.125 cups.