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Edexcel S2 - 27th June 2016 AM Watch

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1. (Original post by SeanFM)
Can't promise anything but I'll look through past papers to see if there is anything interesting that can be made..

(you might want to try the madasmaths stats booklets too).
I'll have a look at madas and pick out a few hard ones!
2. could someone pls help me out with question 7b june 13 R Paper.

https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

I did 20x0.2, which is 4. So i got 4 correct answers, and 16 incorrect answers. So my S value keeps coming to s=16X-16
3. (Original post by bat_man)
could someone pls help me out with question 7b june 13 R Paper.

https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

I did 20x0.2, which is 4. So i got 4 correct answers, and 16 incorrect answers. So my S value keeps coming to s=16X-16
Number of correct answers = X. number of incorrect answers = 20 - X.

number of points from total correct answers = ...

number of points docked from total incorrect answers = ...

hence...

it's not asking for you to find that it's when you get 4 correct answers and 16 incorrect answers (which doesn't quite make sense, though I see what you are trying to do)

It's asking how many points you get when X answers are right. (implying that 20-X are wrong).
4. Woah

I just discovered that the largest possible product of 2 numbers that have a sum of n is (n/2)^2

I might be late, but i feel like a genius

EDIT: I also feel like an idiot for not knowing that before

Woah, i also just found out the highest possible product of X numbers that have a sum of n is (n/x)^x
5. When finding th criticL region do you fin the closest or the smaller value June 13 3b does not do the closet but I normally always pick the closet
6. Has anyone got the list of previous boundaries?
7. If X is binomially distributed:

Does B(X <= 6.9) = B(X <=6)

?
8. (Original post by iBall)
Has anyone got the list of previous boundaries?
which year are you after?
9. (Original post by alvosm)
hi guys i nearly always get the boundaries and the sign for the continuity correction wrong. do you guys have any trick or tip on how to do the boundaries bc they are easy marks im losing right now!

any help is much appreciated thankss!!
exam solutions has a video on continuity corrections !
https://www.youtube.com/watch?v=SmjepW2Mb28 - watch all of this

also a tip is to think if its asking for less than then think what value what round DOWN to this e.g. if you've got P( X</equal to 5) then you'd think well 5.5 rounds down to 5 if that makes sense
10. Can someone explain Q3d please

https://ef8b5216a7366459ac0f2ce0ac13...%20Edexcel.pdf

EDIT: Actually I get it now, but how would you go about it
11. (Original post by Superbubbles)
When finding th criticL region do you fin the closest or the smaller value June 13 3b does not do the closet but I normally always pick the closet

(Original post by Armpits)
If X is binomially distributed:

Does B(X <= 6.9) = B(X <=6)

?
Correct. The binomial distribution (a discrete one) takes no values between 6 and 6.9, so those two things are equivalent.
12. Can anyone explain why they're using -1.54 rather than 1.54?

13. Does anyone have a good way/acronym of remembering skewness in terms of mode median and mean?

Im struggling to remember the pattern
14. (Original post by Mattematics)
Can anyone explain why they're using -1.54 rather than 1.54?

using symmetry..the probability that Z is less than 1.54 is 0.938 (3dp) so the probability that it is greater than -1.54 is 0.938
15. (Original post by 13 1 20 8 42)
using symmetry..the probability that Z is less than 1.54 is 0.938 (3dp) so the probability that it is greater than -1.54 is 0.938
I'm an idiot, was thinking of the tables the wrong way round. Thanks!
16. (Original post by SeanFM)
It takes practice (not necessarily of actual questions where you use a CC, just identifying what they would be given an inequality).

You can convert '<' and '>' into less than or equal to and greater than equal signs first, and then just apply the same logic to them, so trying to figure out what to do in 2 cases rather than 4, if you see what I mean.

So if I said, continuity correction - add 0.5 for x less than or equal to something, so that the values above the 'greatest' in the continuous distribution round down to the 'greatest' in the discrete distribution. (continuity correction is )

The other case is >.continuity correction - take away 0.5 for x greater than or equal to something, so that those values round up to the 'least in the discrete distribution.
(continuity correction is )

The other two cases are greater than or equal to and less than or equal to, but they're like the two ones above, just without the first step.
thank you very much!!!
17. can anyone explain this?

18. does anyone know where i could find a good video explaining the difference between the probability density function and the CDF.?
19. (Original post by Yua)
can anyone explain this?

X <k/2 means that X < k, so we can just write it as X < k/2.
20. (Original post by Yua)
can anyone explain this?

The probability of less than k/2 intersection less than k is the same as just less than k/2.

I.e., probability of x being less than 0.5 and less than 1 is just the probability of it being less than 0.5.

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