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Edexcel S2 - 27th June 2016 AM

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1. (Original post by NamelessPersona)
I just said that it had to be discrete and a whole number and put 225
Oh okay nice

(Original post by Music With Rocks)
I put 342.25 as my final answer
342.25 would only have worked if you took the negative square root of it in the normal distribution expression which i considered but it seemed too specific
2. (Original post by exclamationmark)
How did people get 225? I ended up solving the quadratic p^2 + 0.7p - 55.5 <0 something like that 🙈
It was n and sqrt(n) so the roots of the quadratic are equal to the sqrt of n and then you square the positive one as sqrt(x)≥0
3. (Original post by Michaelj99)
I just put 225 in the whole thing and it worked out to get the probability they showed, my friend put both in when u find the z values, and said you get negative z for 342.25 i think? you didn't really have to say why you picked what?
Yeah I subbed back in and you do get -Z, somehow didn't think to take the other root :/ hoping I get 6/8 or so for method marks
4. (Original post by Michaelj99)
I just put 225 in the whole thing and it worked out to get the probability they showed, my friend put both in when u find the z values, and said you get negative z for 342.25 i think? you didn't really have to say why you picked what?
Basically 342.25 would have worked if you took the negative square root at the bottom but idk

I think and hope it's 225 cause that worked flawlessly when i plugged it back in and it only asked for 1 value
5. Can someone please explain what I did wrong as I can't see it! I got n=271!

6. (Original post by lovecupcakes1997)
[5,9]
I did 5^2pi = 25pi and 9^2pi = 81pi
Then i wrote [25pi,81pi]
E(X) = 1/2(25pi+81pi)
= 53pi
That's exactly what I did, pretty sure we were wrong though :/ Oh well, hopefully at least 2 marks.
7. (Original post by gameofthrones1)
Can someone please explain what I did wrong as I can't see it! I got n=271!

You expanded (55.5 - 0.2n)^2 incorrectly
8. Hey guys for the 8 mark question i got n=62 which i know is wrong, but i want to know how much marks you think i could get, because i made a mistake when squarerooting 0.16n so i didnt do the quadratic equation
9. (Original post by apzoe)
Guys what values did you get for a, b and k?
What did you get

I only did k and b , b is 8 as given and k is 1/9

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10. (Original post by gameofthrones1)
Can someone please explain what I did wrong as I can't see it! I got n=271!

You've written 1.75 then changed it to 1.45
11. (Original post by exclamationmark)
How did people get 225? I ended up solving the quadratic p^2 + 0.7p - 55.5 <0 something like that 🙈
You get 555-2p=7sqrtp and if you square all of that then you got 4p^2 -2269p + 555^2 =0 and then if you solve it using the quadratic function you get two answers 225 and something else with a point 25 in and as you were finding n it had to be a whole number so 225 was the answer
12. (Original post by NamelessPersona)
You expanded (55.5 - 0.2n)^2 incorrectly
How many marks out of 8 do you think this would score, i made the same mistake :/
13. (Original post by yasamin3)
Hey guys for the 8 mark question i got n=62 which i know is wrong, but i want to know how much marks you think i could get, because i made a mistake when squarerooting 0.16n so i didnt do the quadratic equation
I would say 4, an M1 for using normal approx, an A1 for half cc, and an M1 and A1 for getting to 55.5-0.2n = 1.75*sqrt(0.16n)
14. (Original post by iipebblesii)
You've written 1.75 then changed it to 1.45
My handwriting is quite bad, its 1.75 still haha
15. (Original post by S14151)
How many marks out of 8 do you think this would score, i made the same mistake :/
I'd say at least 4 look at my previous post
16. (Original post by NamelessPersona)
I would say 4, an M1 for using normal approx, an A1 for half cc, and an M1 and A1 for getting to 55.5-0.2n = 1.75*sqrt(0.16n)
Not too bad, thanks!
17. (Original post by NamelessPersona)
You expanded (55.5 - 0.2n)^2 incorrectly
Did I? I thought we didn't have to treat them as bracketed?
18. (Original post by Michaelj99)
I just put 225 in the whole thing and it worked out to get the probability they showed, my friend put both in when u find the z values, and said you get negative z for 342.25 i think? you didn't really have to say why you picked what?
I got 342 too! is it wrong?
19. (Original post by gameofthrones1)
Did I? I thought we didn't have to treat them as bracketed?
If you square both sides you treat it as a bracket
20. how many marks out of 8 just for not appling the continuity correction? everything else was correct just my quadratic was -55 not -55.5

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