<PRE><B>Question 249495</B>
let x = price of the tile.
let y = number of tiles sold each month.


when x = 20, y = 42
when x = 10, y = 52


equation of a straight line in slope-intercept form is:


y = mx+b


m is the slope and b is the y intercept.


to find the slope, use the equation m = (y2-y1)/(x2-x1)


(x1,y1) = (10,52)
(x2,y2) = (20,42)


slope equals (52-42)/(10-20) = 10/-10 = -1


plug this in the general form of the equation to get:


y = -1*x + b


substitute for x and y using either of the two points used to find the equation of the line.


use (20,42)


equation becomes:


42 = -1*(20) + b


solve for b to get:


b = 62


equation of your line is:


y = -1*x + 62


graph of the equation looks like this:


{{{graph(600,600,-10,70,-10,90,-1*x+62)}}}


</PRE>