X~N(15,4)
Find w to 2 d.p.
P(mod(X15) < w ) = 0.9
Im confused. Any help pleeeaase
Stats  Normal DistributionModulus


Expand the modulus bracket inside the probability.

I have, i get stuck @:
P((x15)< w < (x15) )
Next I modelled probability onto Z~N(0,1)
P(((x15)15)/2) < Z < (((x15)15)/2) =0.9
P((x30)/2)P(x/2) = 0.9
P((x30)/2) + P( x/2)  1 = 0.9
P( 1.2815 > w ) = 0.9
(x30)/2 + x/2  1 = 1.2815
rearrage etc
x = 11.521
Plugged ths into P(mod(x15) < w ) = 0.9
w = 3.479
The answer is 3.29
And im not entirely sure you can do half the steps i just used 
Look at it this way, Let Y be a normal random variable such that, Y = X  15, now Y~N(0,4)
And you want P(y<w); This means that the only area you are not looking for is 10.9 = 0.1; but since the normal is symmetric you have 0.05 of that on each side.
So now look up the Z value for a probability of 0.05 and plug it in to the standardization equation: Z = (w  0)/2. This obtains the answer. 
I still do not understand.
Can anyone please go through this question:
If the random variable X is distributed as N(5,4), calculate:
P(modulus(X 5) > 3 ).
Thanks 
(Original post by TheNightmare)
I still do not understand.
Can anyone please go through this question:
If the random variable X is distributed as N(5,4), calculate:
P(modulus(X 5) > 3 ).
Thanks
ok so this is the same as p (x5>3)+p(x5<3)
so its basically p(x>8)+p(x<2)
Still want help with finding w? 
(Original post by TheNightmare)
I still do not understand.
Can anyone please go through this question:
If the random variable X is distributed as N(5,4), calculate:
P(modulus(X 5) > 3 ).
Thanks
P((x  5) > 3) + P((x  5) < 3)
= P(x > 8) + P(x < 2) 
(Original post by falcon pluse)
l,
ok so this is the same as p (x5>3)+p(x5<3)
so its basically p(x>8)+p(x<2)
Still want help with finding w?
So the general rule is:
P(modulus(Xy) > q) = P(Xy > q ) + P(Xy < q) right?
What if it was like this:
P(modulus(Xy) < q) would this be = P(Xy < q ) + P(Xy > q) ? 
(Original post by MathematicsKiller)
This is basically:
P((x  5) > 3) + P((x  5) < 3)
= P(x > 8) + P(x < 2)
According to my text book it is: 0.0668
but i'm somehow getting : 0.1336
What am I doing WRONG??? 
(Original post by TheNightmare)
What is the answer?
According to my text book it is: 0.0668
but i'm somehow getting : 0.1336
What am I doing WRONG???
I get the same answer as you.
I believe the answer in the text book is the answer you would get if there were no modulus. 
(Original post by MathematicsKiller)
Are you sure you posted the question correctly?
I get the same answer as you.
I believe the answer in the text book is the answer you would get if there were no modulus.
Yes the question is P( X5 > 3).
So is the text book answer wrong? 
(Original post by falcon pluse)
l,
ok so this is the same as p (x5>3)+p(x5<3)
so its basically p(x>8)+p(x<2)
Still want help with finding w?
According to my text book the answer is: 0.0668
but I am getting : 0.1336
Is the text book answer wrong? 
I miss statistics

(Original post by littleone271)
I miss statistics
If the random variable X is distributed as N(5,4), calculate:
P((X 5) > 3 ).
Modulus is in BOLD and is Underlined
Thanks 
(Original post by TheNightmare)
Will you be able this question for me:
If the random variable X is distributed as N(5,4), calculate:
P((X 5) > 3 ).
Modulus is in BOLD and is Underlined
Thanks
I remember this book being pretty amazing though because it's got worked examples and everything in it. I had this one for s1b and the s2 and s3 ones and they were all really good.
http://www.amazon.co.uk/AdvancingMa...1519123&sr=11 
(Original post by littleone271)
I used to be good at it and I did an AS in pure statistics but that was a couple of years ago and I havn't really done it properly since so I can't remember how to do it ... Sorry...
I remember this book being pretty amazing though because it's got worked examples and everything in it. I had this one for s1b and the s2 and s3 ones and they were all really good.
http://www.amazon.co.uk/AdvancingMa...1519123&sr=11 
Can anyone answer this?
X~N(5,4)  Calculate: P( X5 > 3 ).
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