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/sci/ - Science & Math

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3962429 No.3962429 [Reply] [Original]

I don't get it, /sci/. I know this is really basic but I'm so confused.

"You are taking a course in high school. You must take 4 tests in this class. The first 3 tests scores were 87, 92, and 84 all out of 100 points. The fourth test you do not know what you got, and it is out of 200 points. These four tests are the only grades in the gradebook. You want at least an A (90%+) for the course. What is the lowest score on the fourth test you can get to make your grade for the course an A?"

I get 97%, but my professor says it is 93.5%. Seriously, why? I can't find anything wrong with 97%, and if I check my answer and 93.5% doesn't work out.

>> No.3962442

>implying a professor set this and not a primary school teacher

>> No.3962448

>>3962442
>lives in america and doesn't call all instructors "professor"
lol

>> No.3962459

>>3962448
>lives in America

lol

Seriously, why would you call a guy who only needs a bachelors a professor?

>> No.3962512

http://www.wolframalpha.com/input/?i=%28450-84-87-92%29%2F2

He's right.

To get 90%+ you need 450 out of the 500(or more) points.
so all the points you earn need to add up to 450.
so you need 450-84-87-92=187 points for the last test.
since the total was 200, and 93.5% of 200 is 187, 93.5% is the right answer.

>> No.3962539

>>3962512
I do it like (.84 + .87 + .92 + x/2)/4 = .9

>> No.3962548

>>3962539
x/200, excuse me

>> No.3962549

>>3962539
you aren't taking into consideration what an average actually is.

>> No.3962553

>>3962549
You add all of the numbers and divide by the number of numbers

>> No.3962601

>>3962539

your x is not worth more in that scenario

you've got to be kidding me

>> No.3962613

>professor
I wish I went to clown college ;_;

>> No.3962614

>>3962539
http://www.wolframalpha.com/input/?i=%28.84+%2B+.87+%2B+.92+%2Bx%2Bx%29%2F5%3D0.9
Note that I added x twice, because it counts towards the final grade twice as much as the other quizzes.
Alternatively: you're allowed to pretend that you made two quizzes that count the same as the others, and that you got an identical result on both of them.
Also note that I divided by 5, because there's 5 values being added now that we added x twice.

>> No.3962763

>>3962429
So the weighting of each test is the number of points? If so you need 450 points to get 90%, you currently have 263 points, therefore you need 187 points 187/200 = .935.

What you did assumed equal weighting of tests.