Need help with Stat2 May 2013 replacement paper edexcel

Hey Guys, I`m stuck with question no. 7b.Trying very hard to understand the mark scheme but seriously it was of no use.Is there anybody out there who can make it very very clear to me.Exam is tomorrow morning,so a very quick respond would be much appreciated...

Hi.

Lets say you had 3 answers correct. Then 20-3, i.e. 17 would be incorrect.
The score would be 4x3-17.

What the mark scheme does is say that if X questions are correct, then there are 20-X incorrect.
The score is then 4X - (20-X) = 5X - 20.

I do not think that the EDEXCEL, June 2013 paper in S2 was ever replaced.

Check out pearson website.

thanks

Hey thank you very much for such a quick respond,but have a question.
If X=3 THEN S=5(3)-20= -5 . So, what does negative 5 means here?:/

Hi. The negative 5 represents the overall score.
3 correct questions, 17 incorrect questions, so 3*4 + (-17) = -5.

Think of the S=5X-20 formula meaning that you don't have to work out the number of incorrect answers before performing the calculation, hence why using it for S=3 as also giving the answer of -5.

p.s. sorry about the late response. I'm not online at home. You'll probably be seeing this after you did your exam, in which case I hope it went well.