# What's wrong with my algebraic expression?

1. Jun 18, 2016

### Terrell

Mentor note: moved to homework forum

A store has been selling 200 DVD burners a week at $350 each. A market survey indicates that for each$10 rebate offered to buyers, the number of units sold will increase by 20 a week. Find the demand function and the revenue function. How large a rebate should the store offer to maximize its revenue?

my expression: R(x) = ($350-$10x)(200+20x)

Last edited by a moderator: Jun 18, 2016
2. Jun 18, 2016

### Staff: Mentor

What did you get for the demand function?

3. Jun 18, 2016

### Terrell

according to my textbook, demand function is also the price function... so i think that should be the ($350-$10x) part of the expression...?

4. Jun 18, 2016

### Staff: Mentor

I think you might be misinterpreting what the book is saying. Price and demand are two different things. Usually the demand is written as a function of the price, p.

According to your first post, when p = 350, the demand d will be 200. And when the price is decreased by \$10, the demand is forecast to be 220.
Assuming that demand is a linear function of price, you should be able to write the demand function from that information.

5. Jun 18, 2016

### Ray Vickson

Why do you think your expression is wrong? Aside from failing to define what you mean by 'x', it looks OK to me, provided that you are extra careful about what 'x' actually means.

Now: what about the rest of the problem?

Last edited: Jun 18, 2016