Question 1109878:  I need help figuring out how to solve this problem. 
 
The cost C of steel tubing is jointly proportional to its length L, in feet, and Diameter D, in inches. If a 9 foot tube with a 1 inch diameter cost $72, find the cost of a 9 ft tube with a diameter of 10 inches. 
 Answer by stanbon(75887)      (Show Source): 
You can  put this solution on YOUR website! The cost C of steel tubing is jointly proportional to its length L, in feet, and Diameter D, in inches. If a 9 foot tube with a 1 inch diameter cost $72, find the cost of a 9 ft tube with a diameter of 10 inches.  
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C = k*L*D 
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Solve for "k" 
72 = k*9*1 
k = 8 
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Equation: 
C = 8*L*D 
C = 8*9*10 = $720 
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Cheers, 
Stan H. 
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