# Thread: direct variation...

1. ## direct variation...

not so good with word problems :/
i know you use the direct variation formulas but sometime u have different situations where you add in other variables

A company has found that the demand for its product varies inversely as the price of the product. When the price is 3.5 dollars, the demand is 500 units. Find a mathematical model that gives the demand in terms of the price in dollars.

y= ___
then approximate the demand when the price is 6.25 dollars.
answer::

& another one i have played around with:

Let

??
i know you have to replace the x's with Y's so that its

x=y+2/y+10 and then a common factor but the rest i forget

2. Originally Posted by bharriga
not so good with word problems :/
i know you use the direct variation formulas but sometime u have different situations where you add in other variables

A company has found that the demand for its product varies inversely as the price of the product. When the price is 3.5 dollars, the demand is 500 units. Find a mathematical model that gives the demand in terms of the price in dollars.

y= ___
then approximate the demand when the price is 6.25 dollars.
answer::
Inversely proportional means
$y = \frac{k}{x}$
where k is a constant.

-Dan

3. Originally Posted by bharriga
Let

??
i know you have to replace the x's with Y's so that its

x=y+2/y+10 and then a common factor but the rest i forget
You do indeed have the correct approach.
$y = \frac{x + 2}{x + 10}$

Becomes:
$x = \frac{y + 2}{y + 10}$

$x(y + 10) = y + 2$

$xy + 10x = y + 2$

$xy - y = 2 - 10x$

$(x - 2)y = 2 - 10x$

$y = \frac{2 - 10x}{x - 2}$

-Dan