Question 205669
For a particular item the supply equation is given by S= 2p+5. At a price of $1, 19 units of this product are demanded. If the demand equation is linear and the demand is 11 units at a price of $3, find the demand equation. 
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D(p) = mp + b
m is the slope and is the increase of demand when p increases 
by $1; so m = 19
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Since demand is 11 when p = $3, and m = 19, you can solve for "b":
11 = 19*3 + b
b = -46
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Demand Equation: D(p) = 19p - 46
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Cheers,
Stan H.