Question 535464
x + y + z = 20
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x = y + z
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z = 3x
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substitute z = 3x
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x = y + 3z
-2x = y
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substitute z = 3x and y = -2x
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x + (-2x) + 3x = 20
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2x = 20
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x = 10
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z = 3x = 30
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y = -2x = -20
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Checking...
x + y + z = 10 -20 + 30 = 20
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Answer:  The three numbers are -20, 10, and 30.
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Done.