Question 287
<pre><font face = "courier new">To produce 80 copies of a magazine costs 52 cents per copy. To produce 760
copies of the magazine costs 35 cents per copy.
a) Name two ordered pairs.<b>
(80,52) and (760,35)</b>
b) Write the linear equation.<b></pre> 
`
Use the slope formula:
` ` `y<sub>2</sub> - y<sub>1</sub>
m = ---------
` ` `x<sub>2</sub> - x<sub>1</sub>
`
with (x<sub>1</sub>,y<sub>1</sub>) = (80,52) and (x<sub>2</sub>,y<sub>2</sub>) = (760,35)
`
` ` ` 35 - 52   -17   -1 
m = --------- = --- = --- = -0.025
` ` `760 - 80   680   40
`
Now use the point-slope formula:
y - y<sub>1</sub> = m(x - x<sub>1</sub>)
y - 52 = -0.025(x - 80)
y - 52 = -0.025x + 2
` ` `y = -0.025x + 54</b>
`
c) Predict the cost per copy for 480 copies.<b>
Substitute 480 for x in that equation
` ` `y = -0.025(480) + 54
` ` `y = 42
`
Edwin <font face = "wingdings" color = "red" size = 6>J</font>