Sorry for all the post, but I don't have access to a tutor to blow past this stuff quickly..

When they say 100 = 3000/2(10)+a, they "magically" change it to 100(20+a)=3000 to make it easier to solve. How do they know they can do this?

For cartridges sold at per cartridge, (since is the number of cartridges sold,in thousands) and . Substituting into the equation yields

.

Solving this equation for yields

.

Since is a constant, the function can be written as . To determine how many cartridges will be sold at per cartridge, you need to evaluate . Since is given in thousands, there will be cartridges sold at per cartridge.When they say 100 = 3000/2(10)+a, they "magically" change it to 100(20+a)=3000 to make it easier to solve. How do they know they can do this?

How the heck did they turn 100 into 20 and 3000 into 300? How did they know to do that?

We'll start there.. I know this is very simple, but I learn awfully on the computer & when I have too much time to confuse myself because I can't ask right away. Lol.. Keep that in mind when explaining.