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