Question 173563
Suppose you have a lemonade stand, and when you charge $1 per cup of lemonade you sell 50 cups. But when you raise your price to $2 you only sell 25 cups. Write an equation for the number of cups you sell as a function of the price you charge. Denote "C" for number of cups, and "P" for the price you charge. Assume the function is linear. 
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You have two points: (1,50) and (2,25)
slope = (25-50)/(2-1) = -25
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Form: y = mx+b
intercept: 50 = -25*1 + b
b = 75
Equation:
C = -25p + 75
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Cheers,
Stan H.