Making realistic scenarios for the given lines

1. Apr 20, 2016

Kirito123

1. The problem statement, all variables and given/known data

9. Suggest a realistic scenario that could be modelled with each of the following equations. Be sure to define each variable, including units.

2. Relevant equations

y=mx + b

3. The attempt at a solution

a. y = –65x + 200

To stay at a private golf course, you have to pay a total of $2500. But, the private golf course has a deal that says if you purchase a membership for the golf course, which costs$200, $65 of the total cost will be deducted per day. In the equation, y represents the total cost, -65 represents the discount of the member ship (a$65 deduction), x represents the number of days spent at the golf course after purchasing the membership, and $200 is the total cost of the membership. b. y = 3.5x + 10 A local car wash charges a total of$3.5 per car wash, with an additional fee for extra services. In the equations above, y represents the total cost of the car wash, 3.5 represents the total cost per car wash, x represents the number of car washes, and 10 represent the additional fee for extra services.

I understand what I have to do and I know I'm doing it correctly, just wanted to know if the 2 examples I gave for each line made sense. Since it has to be realistic I can't have a scenario that doesn't sound realistic.

2. Apr 20, 2016

Staff: Mentor

What happened to the $2500? If y represents the total cost, spending 10 days leads to total "costs" of -$450?
Shouldn't you pay more for extra services if you wash your car more often? That is a cheap car wash by the way.

3. Apr 29, 2016

Kirito123

hmm aren't car washes cheap sometimes, and that would bring in more customers and make them more money?

4. Apr 29, 2016

Staff: Mentor

Well, google some prices. But that is not the main point I think. The additional services cost more if you wash your car more often.

5. Apr 29, 2016

Kirito123

They do?? i hardly ever go to the car wash so i have no clue. I just made this problem up and to me it made sense. Since i can only use this formula for b to make my problem "y = 3.5x + 10", does that mean that my problem isn't realistic and i should try to make a new one??

I think i get what you mean since if you stay longer the cost goes into negatives which means they have to pay you lol. So if i did this would that make more sense:

(anything bold is what I added, which is pretty little)

To stay at a private golf course for only 1 week, you have to pay a total of $2500. But, the private golf course has a deal that says if you purchase a membership for the golf course, which costs$200, $65 of the total cost will be deducted per day. In the equation, y represents the total cost, -65 represents the discount of the member ship (a$65 deduction), x represents the number of days spent at the golf course after purchasing the membership, and $200 is the total cost of the membership. 6. Apr 29, 2016 mfb Staff: Mentor What about some base price for providing a service in general and an additional fee based on actual use? Many systems work like that. Same question again: What happened to the$2500? You always pay more than $1000, something your formula does not reflect. 7. Apr 29, 2016 Kirito123 wait what your saying is that im not stating what 2500 is? since i said it was the total would that means 2500 is y since its the total amount? 8. Apr 29, 2016 mfb Staff: Mentor With your golf scenario, staying for one day costs$2500+$200-$65 = $2635, staying for 7 days costs$2500+$200-7*$65 = $2245 None of those values match your function y = –65x + 200, which predicts y=135 for x=1 and y=70 for x=2. 9. Apr 29, 2016 Kirito123 wait i think you might have misunderstood, staying for 1 week not 1 day. so it would be$2500 + $200 - 65 =$2635 this is for the whole week you stay.

10. Apr 29, 2016

Staff: Mentor

If you stay for a fixed week, then there is no free variable at all?

You said "$65 of the total cost will be deducted per day", that would indicate 7*$65 for a week.

That golf scenario won't work.

11. Apr 29, 2016

Kirito123

a free variable? sorry but isn't there not suppose to be a free variable?

12. Apr 29, 2016

MullaTheMech

Car wash:
Y can equal the car wash price.
Would it work if you switched the explanation for m and b
I'd like going to the carwash more if the extra services cost less than the actual wash. It would make me want to get multiple extra services.

I think scrapping the golf course idea would be quicker than trying to make it fit
Here you say y=2500
10 is what mfb used so x=10 for 10 stays at the course
2500=-65(10)+200
2500=-650+200
2500=-450

13. Apr 29, 2016

Staff: Mentor

In the "you have to book 1 week at the golf course", what is x?
You have a function "y as function of x", that doesn't make much sense if there is only one possible value of x.

14. Apr 29, 2016

Kirito123

x is the total amount of days spent at the golf course right?

15. Apr 29, 2016

Staff: Mentor

Then your function would have to produce meaningful results for e. g. x=1.
1 day spent at the golf course => y = 200-65*1 = 135. So who pays \$135?

As I said before, the golf course example for that equation does not work. Try to understand why it does not work, but it won't get fixed.

16. Apr 29, 2016

Kirito123

O i see so i will forget the whole thing in general and start a new problem that makes sense.