Posted by **Daniel** on Thursday, March 7, 2013 at 10:20am.

In the quiz in Exercises 1 and 2, the grading scheme is as follows: each right answer is awarded 5 points, and 1 point is taken off for each wrong answer. Recall that the quiz consists of 10 questions, and that in the class, the average number of right answers is 6.2 and the SD of the number of right answers is 1.4. In what follows, it will help to express a student’s score in terms of the number of right answers the student got.

(1) Find the average score of the class.

(2) Find the SD of scores of the class.

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**EDXStudent**, Thursday, March 7, 2013 at 1:23pm
Dude.

Stop violating the honor code.

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**EDXStudent**, Monday, March 11, 2013 at 12:59pm
I help regulate the honor code by searching for keywords.

I'm allowed to do so.

It helps the staff @ edX, and maintains the integrity of the course.

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**EDXStudent**, Monday, March 11, 2013 at 1:02pm
And anyways, I already finished the problem set.

So what is there for me to gain from searching for answers?

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**EDXProfessor**, Wednesday, March 13, 2013 at 2:22am
Here is an idea, not the answer:

S[i] = 5*Xr[i] - 1*Xw[i], where S[i] is Score, Xr[i] - right answer and Xw[i] - wrong answer for the i-th student

The key here is to remember that there are exactly 10 questions each student answers, so Xw[i] = 10 - Xr[i]

Which gives us the following affine transformation:

S[i] = 6*Xw[i] - 10

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