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# Edexcel S3 - Wednesday 25th May AM 2016 watch

1. Well done Edexcel. I lost two marks on the 2015 IAL because I didn't write out my explicit values of O^2/E. How unthinkable that someone might just put it straight into their calculator! Clearly penalising people for such a colossal and irrecoverable error will further aid discriminating students by ability.

I think I'd better just do all the multiplications and divisions using the grid method in my work so Edexcel can be so benevolent to give me the method marks for multiplication techniques (at least two terms shown; this mark is not necessarily implied by a correct final answer).

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2. (Original post by AakashG)
...
Not relevant to S3.

this was my logic:

- mean is 2 per minute
- mean is 10 per 5 minutes
- mean is 300 per 5 minutes for 30 days <- or can you not scale up like that because its different days combined?
I'll have to admit to being overly cheeky here, didn't bother reading the question and just guessed at what you were talking about.

(a) looks like a mess and the solution to it seems like it's answering a totally different question. I would just ignore it and move on if I were you, seems like a mistake to me.

also, im still really confused, 8b) isnt that a basic poisson question, like why do we need to use CLT?
Because it's asking for the probability that the mean number of calls in the five minute interval, that is, you want to find a distribution for the mean number of alls. This means you need to use the CLT, it's not a basic poisson at all, that would be find the probability that the number of calls (see that I didn't use the word mean) is less than x.

(Original post by SeanFM)
it can be fairly draining when you see similar/the same questions being asked by different people, it's like they come and go but you're always there and it's not an easy thing to do.
That's a very good way to put it, hit it right on the nose!

Mixed bag, we shall see but the summer is now mine to enjoy.
Ah, nice nice. Did well in the stats modules, I'd wager? Those seem to be your forte.

I see you have Physics/FPs next month - feeling prepared?
Fairly confident for the FP's, not so much about Physics.
3. (Original post by cjlh)
Question: for the hypotheses in Spearman's rank questions, should you write them in both words and in terms of rho? E.g. "There is no association between the two variables (rho = 0)"
Careful! When talking about Spearman and pmcc never use the word association. CORRELATION is the correct word to use. Association is for contingency tables. There is an important distinction to be made between those. And no, you should should write them just in terms of symbol.
4. (Original post by Krollo)
Well done Edexcel. I lost two marks on the 2015 IAL because I didn't write out my explicit values of O^2/E. How unthinkable that someone might just put it straight into their calculator! Clearly penalising people for such a colossal and irrecoverable error will further aid discriminating students by ability.

I think I'd better just do all the multiplications and divisions using the grid method in my work so Edexcel can be so benevolent to give me the method marks for multiplication techniques (at least two terms shown; this mark is not necessarily implied by a correct final answer).

Posted from TSR Mobile
iniiitt proper pain in the arse how i have to write out every value and then retype it all in full into my calculator so i dont miss out an rounding accuracy but have to show them for method marks
5. (Original post by Zacken)
Careful! When talking about Spearman and pmcc never use the word association. CORRELATION is the correct word to use. Association is for contingency tables. There is an important distinction to be made between those. And no, you should should write them just in terms of symbol.
Well I'm very glad you've made that clear then Thanks a lot, been self-teaching so I might have glossed over some things I shouldn't have. Cheers!
6. (Original post by Krollo)
Well done Edexcel. I lost two marks on the 2015 IAL because I didn't write out my explicit values of O^2/E. How unthinkable that someone might just put it straight into their calculator! Clearly penalising people for such a colossal and irrecoverable error will further aid discriminating students by ability.

I think I'd better just do all the multiplications and divisions using the grid method in my work so Edexcel can be so benevolent to give me the method marks for multiplication techniques (at least two terms shown; this mark is not necessarily implied by a correct final answer).

Posted from TSR Mobile
Hi, just to clarify, how exactly would you set out your working for these q's to gain all the marks?
7. (Original post by connorbarr)
iniiitt proper pain in the arse how i have to write out every value and then retype it all in full into my calculator so i dont miss out an rounding accuracy but have to show them for method marks
how many dp? I normally work out Oi^2/Ei and leave it as a fraction and do sigma of the general fraction and then output the answer.
8. A list of decent book exercises in case anyone wants to take a look:

Ch 1: Ex-1A: 7(d), 8-12, Rev 1: 4, 9, 18, 19

Ch-3: Ex-3A 3(i)Ex-3B 6, 7Ex-3C 5, 6, 7Ex-3D 4, 5, 6, 7, 8, 11, 12Ex-3E 13, 16Ex-3I 6, 8, 10, 17

Found it from my friend
9. Doing goodness of fit in normal distribution, the first class is always p(z<b)-0.000?

I am not sure if the question is clear here
10. estimate limits, to 2 decimal places, between which 90% of the weights of the tubs lie,

june 02 - i got this right but want to double check, it didn't ask anything about the sample mean so i didnt use the standard error and instead used the basic sd. Is that right?
11. (Original post by tazza ma razza)
how many dp? I normally work out Oi^2/Ei and leave it as a fraction and do sigma of the general fraction and then output the answer.
i use (Oi-Ei)^2/Ei and i just work out each value to either 3s.f. or 3d.p. depends what is appropriate, but then when i work out the sum i just type re-type it all into my calculator because rounding loses accuracy init
12. (Original post by tazza ma razza)
estimate limits, to 2 decimal places, between which 90% of the weights of the tubs lie,

june 02 - i got this right but want to double check, it didn't ask anything about the sample mean so i didnt use the standard error and instead used the basic sd. Is that right?
Yep
13. (Original post by Geraer1)
Doing goodness of fit in normal distribution, the first class is always p(z<b)-0.000?

I am not sure if the question is clear here
its probability of less than b, value from the tables
14. In what instances would we want to use the Central Limit Theorem? Like when does it come in handy?

Im worried i'm forgetting everything before the exam
15. (Original post by connorbarr)
its probability of less than b, value from the tables
Yeah I was asking if in the first row the second value of probability is always 0.000? Sorry my question isnt really clear. See attachment
Attached Images

16. How do you go about calculating unbiased estimate of variance from a frequency table.
17. (Original post by Katiee224)
In what instances would we want to use the Central Limit Theorem? Like when does it come in handy?

Im worried i'm forgetting everything before the exam
Taking a sample mean from a population and tests on two means from populations etc.
CLT assures normal distribution.

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18. (Original post by Krollo)
Well done Edexcel. I lost two marks on the 2015 IAL because I didn't write out my explicit values of O^2/E. How unthinkable that someone might just put it straight into their calculator! Clearly penalising people for such a colossal and irrecoverable error will further aid discriminating students by ability.

I think I'd better just do all the multiplications and divisions using the grid method in my work so Edexcel can be so benevolent to give me the method marks for multiplication techniques (at least two terms shown; this mark is not necessarily implied by a correct final answer).

Posted from TSR Mobile
This is why edexcel are winning in life.
They have no clue what actual maths is.
So each individual thing is needed?
I write out the sum normally but not each value of each term n i use the other formula normally

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19. (Original post by Geraer1)
Yeah I was asking if in the first row the second value of probability is always 0.000? Sorry my question isnt really clear. See attachment
well i suppose Zacken can u explain lad
20. (Original post by connorbarr)
well i suppose Zacken can u explain lad
Yeah no problem thank! I think the answer if yes, but I am not sure...

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