Qualification > Math

S1 and S2 DOUBTS HERE!!!!

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mdwael:

--- Quote from: igext on May 19, 2011, 10:33:45 am ---hello
i just have one question
June 2008 Q7(c)
question about normal dist.
I dont get why they are multiplying by 3?
Thank you loads in advance.

--- End quote ---

Because you are picking 3 bags at any order. so you can go like this. let the bag which is less than 53 be A and if its more than 53 be B.
They want 2 Bs and 1 A,

If they are chosen at random the arrangement can come

 B B A

 B A B

 A B B

so there are 3 ways of getting 2 bags which weigh more than 53 and one bag which weighs less. so you multiply the probabilities and then add them or just find the probability once and multiply it by 3. Hope this helps.

Tohru Kyo Sohma:
ok...i have my s1 exam coming(i mean we all do :P)...so i have a few doubts.......its from may/june 2007 qns 1....i dont get it at all

**RoRo**:

--- Quote from: mimiswift on May 19, 2011, 06:11:41 pm ---ok...i have my s1 exam coming(i mean we all do :P)...so i have a few doubts.......its from may/june 2007 qns 1....i dont get it at all

--- End quote ---

For part a)
r=Sxy/?(SxxSyy) = -808.917/?(113573 x 8.657) = -0.816 (3sf)
and by the way, the formula is given in the formula booklet.

b) Since the product moment correlation coefficient is a negative value, then this means that as one value increases, the other value decreases, so in this case, the houses become cheaper as they become further away from the station.

c) The product moment correlation coefficient is not affected by coding i.e. if you add, subtract, multiply or divide the original data for coding, it'll not change, so it's value is the same.

Tohru Kyo Sohma:
wait.....is this page for edexcel paper???....because im doing CIE!!!opsie :-[

Ghost Of Highbury:

--- Quote from: mimiswift on May 19, 2011, 06:11:41 pm ---ok...i have my s1 exam coming(i mean we all do :P)...so i have a few doubts.......its from may/june 2007 qns 1....i dont get it at all

--- End quote ---

Let x = t - 35

Therefore, Mean = -15/12 = -1.25
However, this is the mean for (t-35)

The mean for t = -1.25 + 35 = 33.75 ~ 33.8

The s.d for x (i.e t-35) is the same as the s.d for t

So, S.d =

= = 2.3

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