Need help with y-intercept problem: "It takes Mrs. Wilson 5 minutes to grade a test."

[nickb]

Need help with y-intercept problem: "It takes Mrs. Wilson 5 minutes to grade a test."

I have to find the slope intercept formula and the question is:

It takes Mrs. Wilson 5 minutes to grade a test. If she has 120 students how long with it take to grade all tests?

I think it is y=5x+120 but I am second guessing myself.

 

[ksdhart2]

Erm... if what you've posted is the full and exact text of the problem, quoted word-for-word, then there's no need to use the slope intercept formula at all. The problem states that Mrs. Wilson takes 5 minutes to grade a test. Given no other information, it seems logical to assume that it takes her exactly the same amount of time for each test she grades. So, if she grades 2 tests, how long will it take her? If she grades 5 tests? 10 tests? How did you calculate these answers? Can you use that logic to determine how long it would take her to grade 120 tests?

 

[nickb]

It is a slope intercept (y=mx+b.) real life problem and I need to graph it and create a x and y table. I am going with the y=5x+b. Since 5 is rate/time which would make 120 the y-intercept. I was thinking the y-intercept might be 0 but went brain dead.

Thanks

 

[ksdhart2]

Personally, I'd say that given this is a "real life problem," and not a homework exercise, to use whatever method you find easiest. For me that would be just to simply multiply it out. However, if, for whatever reason, you're just dead set on using the slope intercept method, it can be done that way. You know that you'll be making an equation of a line, and the y-intercept is where it crosses the y-axis. Evaluating your proposed solution, how many minutes would it take Mrs. Wilson to grade 0 tests (i.e. what is the value of y = 5x + 120 when x = 0)? Does that make sense logically? Why or why not? Based on thinking through the problem, how many minutes does it make sense for Mrs. Wilson to take to grade 0 tests? What does that suggest the y-intercept should be?

 

[Steven G]

I have to find the slope intercept formula and the question is:

It takes Mrs. Wilson 5 minutes to grade a test. If she has 120 students how long with it take to grade all tests?

I think it is y=5x+120 but I am second guessing myself.

To see if you are correct you have to know what YOU are saying.
What does YOUR x mean? What does YOUR y mean? What does it mean for x to say be 1. Is the corresponding y correct?

Let x = the number of exams. Let y = how long it takes to grade x exams.

I would hope that you know that if each exam takes 5 minutes to grade and there are 0 exams to grade then it will take 0 minutes to grade these exams. That is, when x=0 we have y=0. Hence the y-int is 0.

Every time you increase the number of exams by 1 how much longer does it take to grade these exams? The answer to this question is the value of the slope m. So you have the y int and you should now know how to find m. So equation is....?