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# Edexcel S1 - 15th June, 2016 [Exam Discussion] watch

1. whats the formula for standard deviation? i googled it and like 50 different variations came up
2. (Original post by KloppOClock)
whats the formula for standard deviation? i googled it and like 50 different variations came up

This is the most used formula, but the formula for V and SD is slightly different when you are working with Discrete Random Variables/Normal Distribution. Check the Edexcel S1 summary page at the end of each chapter to be sure.

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3. I dont get question 4 part d
https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf

Question is what is the probability of some studying SnDnN given that they study SnN.

So that is P(SnDnN | SnN) which = P(SnDnN n SnN) / P(SnN)

which = (4/180) / (36/180) = 1/9

however the answer says its 1/10
4. (Original post by KloppOClock)
I dont get question 4 part d
https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf

Question is what is the probability of some studying SnDnN given that they study SnN.

So that is P(SnDnN | SnN) which = P(SnDnN n SnN) / P(SnN)

which = (4/180) / (36/180) = 1/9

however the answer says its 1/10
There are 40 people who do SnN and of those 40, 4 do all three, so its 4/40=1/10
5. (Original post by 4nonymous)
There are 40 people who do SnN and of those 40, 4 do all three, so its 4/40=1/10
but why isnt it conditional
6. (Original post by KloppOClock)
but why isnt it conditional
Have a look on exam solutions he explains how to work it out.
7. (Original post by 4nonymous)
Have a look on exam solutions he explains how to work it out.
i did he just briefly said what the other guy above said
8. (Original post by Philip-flop)
Well you already know that the question is asking what the probability of her phone lasting 133 hours is. Think about it this way....

P(not need charging after 133 hours)
= P(L>133 | L>127)
= _P(L>133)_
P(L>127)

^It's probability after 133 hours because why would she want to charge her phone before her flight is over!

Hope this helps
Yeah thanks that helped a lot
9. when you go to find the sum of x^2, sum of y^2, sum of xy etc. would you get penalised for doing it using your calculator. What I mean is, would you get penalised for not working out the squares of every x and adding them up, because i feel that its easier and quicker to just stick your data into your calc on stat mode, and work it out that way
10. (Original post by ishaniss)
when you go to find the sum of x^2, sum of y^2, sum of xy etc. would you get penalised for doing it using your calculator. What I mean is, would you get penalised for not working out the squares of every x and adding them up, because i feel that its easier and quicker to just stick your data into your calc on stat mode, and work it out that way
Well its always useful to show your method, look at the mark schemes and see if marks are awarded for methods or just answers
11. What's the difference between being not independent and mutually exclusive?
12. (Original post by KloppOClock)
I dont get question 4 part d
https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf

Question is what is the probability of some studying SnDnN given that they study SnN.

So that is P(SnDnN | SnN) which = P(SnDnN n SnN) / P(SnN)

which = (4/180) / (36/180) = 1/9

however the answer says its 1/10
You've calculated wrong probably due to the venn diagram misleading you

Remember there is 40 people do S&N not 36

So P (S&N&D/ S&N) = 4/40
13. (Original post by physicsamor)
You've calculated wrong probably due to the venn diagram misleading you

Remember there is 40 people do S&N not 36

So P (S&N&D/ S&N) = 4/40
thank you!
14. (Original post by KloppOClock)
thank you!
No problem, I made the same mistake and I just had to read through it a few times because no solutions were helping me
15. Hi, I was wondering if anyone could answer a few questions I had:

1. What sorts of things might we be asked about statistical models and what do we need to know?

2. What functions of the fx-991ES PLUS calculator can we use in the exam

3. What's the difference between mutually exclusive events and independent events or is there non?
16. (Original post by apparently_anerd)
Hi, I was wondering if anyone could answer a few questions I had:

1. What sorts of things might we be asked about statistical models and what do we need to know?

2. What functions of the fx-991ES PLUS calculator can we use in the exam

3. What's the difference between mutually exclusive events and independent events or is there non?
3. MEE p( a and b) = 0
Independant: p(a and b) = p(A) times p(B)
17. (Original post by apparently_anerd)
Hi, I was wondering if anyone could answer a few questions I had:

1. What sorts of things might we be asked about statistical models and what do we need to know?

2. What functions of the fx-991ES PLUS calculator can we use in the exam

3. What's the difference between mutually exclusive events and independent events or is there non?

2. There are a lot of things you can do on your calculator. You can work out:
mean
variance
standard deviation
sum x^2, sum y^2 etc
Normal distribution
18. Effects of coding on Sxx, Syy & Sxy?

Edit:

Sxx has the same effect as variance

Sxy has the same effect as standard deviation
20. (Original post by Pink1998)
doesn't exist

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