Suppose that 6.5 million lbs of coffee are sold when the price is $8.00 a lb. and 4.0 millions lbs are sold when it is $9.00 per pund.

Find a linear function that expresses the amount of coffee sold as a function of the price per pound

Solution:

The price per pound:x

The amount of coffee sold: y million

We assume y = ax + b

And (8, 6.5)and (9,4) is on the line

So

8a + b = 6.5

9a + b = 4

a = -2.5

b = 26.5

So the equation is

y = -2.5x + 26.5

x: price per pound

y: amount of coffee sold(in million)