Qualification > Math
S1 and S2 DOUBTS HERE!!!!
**RoRo**:
--- Quote from: Fidato on April 13, 2011, 12:45:20 pm ---(7) (c)
For this you need to find out the probability that the bag weighs more than 53 kg.
(a)
More than 53, so (53 + 0.5 = 53.5)
53.5 - 50
Z = ------------
2
= si (1.75)
= 0.9599
Now, it's greater then 53, so :
1 - { si (1.75) }
= 1 - 0.959
= 0.0401
(c)
2 bags greater than 53 kg and 1 less than 53 kg .
Probability that any bag is greater then 53 kg = 0.0401
and
Probability that it is less then 53 kg = 0.959
So :
3C2 X (0.401)2 X (0.959)
= 0.004630586
= 0.0046
--- End quote ---
The answer is wrong, the mark scheme is here: http://www.xtremepapers.net/Edexcel/Advanced%20Level/Mathematics/2008%20June/S1%20june%2008%20ms.pdf
**RoRo**:
--- Quote from: Fidato on April 13, 2011, 12:49:10 pm ---(6) (b)
Weights between 190 and 210 are 60 %.
Now 60 % is equal to 0.6 of the probability right. So find out the value of si (0.6) which is equal to 0.7257 .
Now you know the formula :
X - mean
Z = -------------
standard deviation
Let standard deviation be s.
So :
210 - 200 190 - 200
------------ - ------------ = 0.7257
s s
10 - (-10)
----------- = 0.7257
s
20 = 0.7257s
s = 20/(0.7257)
standard deviation = 27.55959763 (or 27.56)
(c)
Use the same formula of normal distribution.
If you will use the original value of standard deviation (that is 27.55959763 and not 27.56), you will be benefited.
180 - 200
---------------
27.55959763
= si (-0.7257)
= 1 - { si (0.726) }
= 1 - 0.766
= 0.234
So 0.234 is the probability that the customer will complain.
--- End quote ---
The answer is also wrong, the mark scheme is here:
http://www.xtremepapers.net/Edexcel/Advanced%20Level/Mathematics/2008%20Jan/6683_01_rms_20080306.pdf
**RoRo**:
--- Quote from: ~Alpha on April 13, 2011, 05:26:33 pm ---Apologies. I wasn't in my right state of mind. -.-
--- End quote ---
No problem! :)
Arthur Bon Zavi:
--- Quote from: The Secret on April 13, 2011, 06:54:58 pm ---The answer is wrong, the mark scheme is here: http://www.xtremepapers.net/Edexcel/Advanced%20Level/Mathematics/2008%20June/S1%20june%2008%20ms.pdf
--- End quote ---
In (a) there was a mistake so part (c) was influenced.
I took +0.5, so things happened.
You just find out the value of Z without adding (0.5) to 53, because at the end you have to subtract it from 1 anyhow.
I hope you understood and will do the (c) part yourself.
Arthur Bon Zavi:
--- Quote from: The Secret on April 13, 2011, 06:55:40 pm ---The answer is also wrong, the mark scheme is here:
http://www.xtremepapers.net/Edexcel/Advanced%20Level/Mathematics/2008%20Jan/6683_01_rms_20080306.pdf
--- End quote ---
Oh ! I now realised that I had taken si (0.6) and not si-1 (0.6).
Anyways I think you got that (+-) method that they have used. Actually P(X<210) = 0.8 so they have taken si-1 ( 0.8 ) and nothing else.
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