Question 92237
Tom and David have 480 marbles between them. Tom arranges them in columns with 6 in each column, and David arranges them with 9 in each column. The total number of columns is 72. Express the above information in the form of an algebraic equation.
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Let T be the number of Tom's columns:
Then 6T is the number of marbles Tom has.
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Let D be the number of Dave's columns:
Then 9D is the number of marbles Dave has.
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6T+9D=480
D+T = 72
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Solve the 2nd equation for D to get: 
D = 72-T
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Substitute into the 1st equation to solve for T
6T+9(72-T) = 480
6T+648-9T = 480
-3T = - 168
T = 56 (Tom has 56 columns)
D+56=72
D= 16 (Dave has 16 columns)
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Cheers,
Stan H.
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