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# Edexcel S2 - 27th June 2016 AM watch

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1. (Original post by iMacJack)
We know X represents the correct answer, so by logic, the amount of wrong answers is 20-X

S represents the final score, which will obviously be the amount he gets - amount he loses

So, each correct is 4 points, so it's 4X - 1(20-X)

Which = 5X-20

Because 1 point's lost for a wrong answer
I don't understand, how did you get 4X-1?

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2. Just got 48/75 on June 2014

This exam will be my ruin
3. Hey SeanFM I came across this thread just now and honestly I wish I had bumped into it earlier! Just wanted to say thanks a lot for all the help you are giving as I also had problems with some questions I see on the thread, but it makes sense now with yours and others' explanations. I appreciate you taking time out your day (meh, well night) to help us

And good luck everyone - hopefully we will score high marks on S2!
4. (Original post by Christop)
Just got 48/75 on June 2014

This exam will be my ruin
I just managed to get 59/75 on June ial 2014 still need to do so many more papers

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5. Alrighty guys, I'm off to bed. Good luck to you all, believe in yourself and you will smash it!

I'm guessing this is your last exam so enjoy it while you can.

6. GUYS HELP

So we reject the null hypothesis of p or the mean lies outside the critical region right? If we reject the null hypothesis what does it mean? That the company's claim is justified?

I'm so confused

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7. This is a joke guys. I'm still awake. Can't sleep!

(Original post by кяя)
GUYS HELP

So we reject the null hypothesis of p or the mean lies outside the critical region right? If we reject the null hypothesis what does it mean? That the company's claim is justified?

I'm so confused

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What question are you looking at?

Have you watched the ExamSolutions videos on hypothesis testing?
8. (Original post by undercxver)
What question are you looking at?

Have you watched the ExamSolutions videos on hypothesis testing?
Just any question in general. Yes I've watched all the videos but I still can't grasp the idea.

I guess I'll just guess

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9. (Original post by кяя)
Just any question in general. Yes I've watched all the videos but I still can't grasp the idea.

I guess I'll just guess

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Okay I'll try to sum this up as best as I can.

You reject the null hypothesis which is like an assumption made, but to prove if this assumption is right or not you do hypothesis testing.

You reject the null hypothesis if its not the null hypothesis. This could be a one tail test (say this is a binomial distribution question) p>___ (this is upper tail) and p<___ (this is lower tail. Also you can have the two tail test where p≠___. You need to choose the type of tail test depending on what the question is asking you. Sometimes they give this to you.

Anything else you need help with?

I feel the introductory videos for the hypothesis testing by the ExamSolutions dude really break it down. Maybe watch that video a couple of times, it took me ages to understand it.
10. (Original post by кяя)
Just any question in general. Yes I've watched all the videos but I still can't grasp the idea.

I guess I'll just guess

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Usually you reject/accept depending on your hypothesis and significance level.
For example lets say there is a company who is saying that the probability of their product working is 80% and they tested a sample of 100 products, out of which 62 worked. Stating hypothesis test the companies claim.

Since their is a p and n we know that X is distributed binomially
We want to test the claim that " the probability of their product working is 80%", so logically our null hypothesis would be Ho: p=0.8 , this one is always easy to get, the null you have to read the question in context, but lets say our null is H1: p<0.8 ( so the probability of the product working is less tham the claim). And lets say the siginficance level is 5% (so 0.05).
We will (after stating both hypothesis) need to fine the probability of our variable X being less than or equal to 62 ( depending on question we may need to find the probability of it being more than or equal to 62, its very important to read the question). Using the tables or formulas you find this probability, Now compare it with the significance level. In our case if the probability is less than 0.05 we find the value significant and reject the null, meaning the probaility is actually less than 0.8. If we do not reject the null, then there is enough evidence to support Ho, meaning we assume that p=0.8. Since the companies claim is that p=0.8, depending if we reject or accept we support or deny the claim, logically then if we reject Ho then we deny the claim, if we support Ho we accept the claim.
11. (Original post by кяя)
Just any question in general. Yes I've watched all the videos but I still can't grasp the idea.

I guess I'll just guess

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12. What is the formula for variacne is ti

Do we say that the variance formula isSigma x^2 / n ) - (sigma x / n)^2
13. (Original post by L'Evil Wolf)
What is the formula for variacne is ti

Do we say that the variance formula isSigma x^2 / n ) - (sigma x / n)^2
(X^2)/N - ((x)/(n))^2
14. (Original post by jshep000)
(X^2)/N - ((x)/(n))^2
are N and n different?

Thanks
15. (Original post by L'Evil Wolf)
are N and n different?

Thanks
nah my caps button just messed up basically its x^2 / n minus the (mean)^2
16. (Original post by jshep000)
nah my caps button just messed up basically its x^2 / n minus the (mean)^2
thanks good luck for the exam
17. Good luck everyone!!
18. For uniform distribution and p.d.f., Is P(X=x) always zero? Why? Doesn't the graph have a respective y value for all x?
19. (Original post by pinksmartiee)
For uniform distribution and p.d.f., Is P(X=x) always zero? Why? Doesn't the graph have a respective y value for all x?
Yeah this is true for continuous random variables. Think of it them as like a measurement, for instance with a ruler. You might have a very precise ruler that allows you to know something's length to a high degree of accuracy but there is still a measure of uncertainty. So you can know that, where X is length, a - delta < X < a + delta for instance, where delta is just a very small number, but you can't pinpoint it and say X = a.
20. (Original post by pinksmartiee)
For uniform distribution and p.d.f., Is P(X=x) always zero? Why? Doesn't the graph have a respective y value for all x?
Probability is the area under the graph e.g. P(a<x<b) is the area between a and b. If you're trying to do P(X=x) then the width is 0 so the area is 0.

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