fast food restaurant sells 425 large orders of fries per week at price $2.75 each. A market survey indicates that for each $0.10 decrease in price, sales will increase by 20 orders of fries.

What is the demand function.

I tried doing it, but the way I was told to do it didn't give me the right answer

Question

fast food restaurant sells 425 large orders of fries per week at price $2.75 each. A market survey indicates that for each $0.10 decrease in price, sales will increase by 20 orders of fries. 

What is the demand function.

I tried doing it, but the way I was told to do it didn't give me the right answer

anonymous · Answer

You're told information to find slope; our demand function is written $p=q$ and we're told that for $\Delta p=-0.1$ we have $\Delta q=20$ so our slope is:$$\frac{\Delta p}{\Delta q}=-0.005$$

anonymous · Answer

We're also told a point on your curve, namely $p=2.75,q=245$. Presuming a linear demand function, we have $p=a-bq=a-0.005q$. Plug in and find $a$.

anonymous · Answer

can I show you the way I did it

anonymous · Answer

let p= price of fries 
let n=# of 0.10 decrease 
let x=# of fries sold 

p=2.75-0.10n
x=425+20n 

then I solve for n in the x function and sub it into the p function

anonymous · Answer

but i don't get the books answer