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Helen's Health food usually sells 400 cans of Propac per week while price is $5.00 per can. After playing with prices for awhile Helen has determined that the weekly demand can be found by using this equation: D=600-40P
where d is cans and p is price per can. Will Helen sell more or less Propac if she raises the price? What happens to her sales every time she raises her price by $1?
The slope of the equation is -40
That means the number of cans sold decreases by 40 for every
increase of one dollar in the price.
Try p=0 and then p=1 and see how D changes by -40.