Exercise 27 Page 193

a It is given that an MP3-player cost

$ 499

2003

and

$ 249.99

2009 .

Let the

x -

axis represent the years and the

y -

axis represent the cost of the MP3-player. Using the given information, we can form the following ordered pairs.

(2003, 499) and (2009, 249.99)

Let's plot them on a coordinate plane and draw a line through them. This way we will get the graph describing the situation.

b To find how much the price drops per year, let's calculate the ratio of rise and run of the line. This ratio will be the slope of the line.

Slope = \frac{rise}{run}

First, we need to find the values of rise and run between the points on the graph.

Rise = 249.99 - 499 = - 249.01 Run = 2009 - 2003 = 6 e r w i e i

Now we can substitute these values into the above formula and find the slope.

Slope = \frac{- 2 4 9 . 0 1}{6} = - 41.501666 \dots \approx - 41.5

Thus, the cost of MP3-player drops approximately

$ 41.50

each year.

c Let's now calculate the cost of the MP3-player in

2013

if the trend continues. In order to do that, we need to write an equation that describes this situation. In Part B we found that the slope is

- 41.5 .

Let's substitute the slope and the point

(2003, 499)

y - y_{1} = m (x - x_{1}) ⇓ y - 499 = - 41.5 (x - 2003)

Now we can substitute

x

with

2013 .

By doing so we will get the equation for

y,

which will represent the cost of MP3-player.

y - 499 = - 41.5 (x - 2003)

$x = 2013$

y - 499 = - 41.5 (2013 - 2003)

Subtract term

y - 499 = - 41.5 (10)

y - 499 = - 415

$LHS + 499 = RHS + 499$

y = 84

If the trend continues, the cost of an MP3-player in

2013

will be

$ 84 .

Check Your Understanding p.192

Practice and Problem Solving p.193-195

H.O.T. Problems p.195

Standardized Test Practice p.196

Spiral Review p.196

Skills Review p.196