Question

In 1990 the average family income was about $ 39 , 000 , and in 2010 it was about $ 70 , 768 . Let x = 0 represent 1990, x = 1 represent 1991, and so on. Find values for a and b so that f ( x ) = a x + b models the data A= _____. B=______. What was the average family income in 2005?

Answer 1

Answer:

$f(x) = 1588.4x + 39000$

$f(15) = 62826$

Step-by-step explanation:

Given

In 1990; Income= $39000

In 2010; Income= $70768

Solving (a): An equation in form of f(x) = ax + b

First, we need to determine the slope, a

$a = \frac{y_2 - y_1}{x_2 - x_1}$

Taking y as income and x as year index.

When x = 0; y = 39000

When x = 20; y = 70768

Substitute these values in the above formula

$a = \frac{70768 - 39000}{20 - 0}$

$a = \frac{31768}{20}$

$a = 1588.4$

Next, is to determine the formula using:

$y - y_1 = a(x - x_1)$

Considering :When x = 0; y = 39000, we have

$y - 39000 = 1588.4(x - 0)$

$y - 39000 = 1588.4x$

Make y the subject of formula

$y = 1588.4x + 39000$

Express y as a function of x

$f(x) = 1588.4x + 39000$

Solving (b): Income in 2005

In 2005, x = 15

So:

$f(x) = 1588.4x + 39000$ becomes

$f(15) = 1588.4 * 15 + 39000$

$f(15) = 62826$