Math Help - function word problem

1. function word problem

having trouble with this problem, seems like it should be simple but im just not getting it. when you charge $2 per cup of lemonade you sell 120 cups. when you raise it to$3 per cup you only sell 60. write an equation for the number of cups you sell as a function of the price you charge. denote c for cups and p for price. any helps appreciated. thanks

2. Originally Posted by brandilee
having trouble with this problem, seems like it should be simple but im just not getting it. when you charge $2 per cup of lemonade you sell 120 cups. when you raise it to$3 per cup you only sell 60. write an equation for the number of cups you sell as a function of the price you charge. denote c for cups and p for price. any helps appreciated. thanks
There is no unique solution to this but a straight line can be put through the data as follows:

Put:

c = m p + k

Now when p=2 c=120, so we have:

120 = 2 m + k

and when p=3 we have c=60, so we also have:

60 = 3 m + k

subtract these, to get: 60 = - m or m=-60, and now put this back into the second
to get:

60 = 3(-60) + k

so k = 240.

RonL

3. thanks for you help