The Student Room Group

Normal distribution Q10

stats 12 q10.jpg

I didn't know how to do any of these.

For part i) i tried:

X~ N(1.34, 0.021)
P(x>1.37)
z=(1.37-1.34)/sqrt(0.021)=0.20702

so p(z> 0.20702) = 1- 0.5425 (from the normal distribution tables for 0.20702)

but it was wrong!!

answers are meant to be:
i) 0.077
ii) 0.847
iii) 0.674
iv)1.313m
Reply 1
Original post by 0utdoorz
stats 12 q10.jpg

I didn't know how to do any of these.

For part i) i tried:

X~ N(1.34, 0.021)
P(x>1.37)
z=(1.37-1.34)/sqrt(0.021)=0.20702

so p(z> 0.20702) = 1- 0.5425 (from the normal distribution tables for 0.20702)

but it was wrong!!

answers are meant to be:
i) 0.077
ii) 0.847
iii) 0.674
iv)1.313m



Notice that, your square rooting in wrong, you've being told the standard deviation, the variable should be std deviation squared so X~N(1.34,0.021^2)
(edited 11 years ago)
Reply 2
Original post by Robbie242
Notice that, your square rooting in wrong, you've being told the standard deviation, the variable should be std deviation squared so X~N(1.34,0.021^2)



thanks! I've worked out part i,ii and iii now :smile:

how would I do part iv?
Reply 3
Original post by 0utdoorz
thanks! I've worked out part i,ii and iii now :smile:

how would I do part iv?


P(X<L)=0.1P(X<L)=0.1 Notice that 0.10000... is in the percentage points table, once you standardise using the z formula, try to inverse the z results (i.e. negative)
Reply 4
Original post by Robbie242
P(X<L)=0.1P(X<L)=0.1 Notice that 0.10000... is in the percentage points table, once you standardise using the z formula, try to inverse the z results (i.e. negative)



by standardising using the z formula, do you mean p(x< (L-1.34)/0.021) =0.1?
Reply 5
Original post by 0utdoorz
by standardising using the z formula, do you mean p(x< (L-1.34)/0.021) =0.1?


Yup then make L1.340.021=z\dfrac{L-1.34}{0.021}=-z if that helps (find z on the percentage tables)

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