Question

Your friend has $100 when he goes to the fair. He spends $10 to enter the fair and $20 on food. Rides at the fair cost $2.00 per ride. Which function can be used to determine how much money he has left over after x rides?

f(x) = -2x + 70
f(x) = 2x + 70
f(x) = -2x - 70
f(x) = -30x + $100

Answer 1

How many dollars does your friend have if he goes on no rides?

Answer 2

70

Answer 3

I believe it is -2x+70

Answer 4

You sure?

Answer 5

Okay, so $70 can be thought of as the intercept and the slope is the marginal cost of each ride. So for every ride the total cost will go down. After how many rides would our friend run out of money?

Answer 6

35 rides

Answer 7

So the equation for money left is equal to $70 minus $2 for every ride

Answer 8

yes?

Answer 9

So it is f(x)= -2x+0?

Answer 10

70*

Answer 11

Right. It would have been more straightforward if they had offered:
f(x) = $70 - $2x but that is the same.

Answer 12

Thanks