Question on Determing the Proportion

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May 18th 2009, 11:11 PM
chobozor

Question on Determing the Proportion

Can someone please help me on this problem with A,B,C,D with explanation please. Thank you in advanced! (Nod)

Data from the national Vital Statistics Report reveal that the distribution of the duration of human pregnancies is approximately normal with mean = 270 and standard deviation = 15. Use this normal model to determine the proportion of all pregnancies that come to term in:
A) less than 244 days
B) more than 275 days
C) over 300 days
D) between 260 and 280 days
May 18th 2009, 11:56 PM
Rapha

Hello.

Quote:

Originally Posted by chobozor

i really need help on these problems !

Quote:

A) less than 244 days
B) more than 275 days
C) over 300 days
D) between 260 and 280 days

A) You need to find $P(X \le 244)$

B) $P(X \ge 244) = 1 - P(X \le 244)$

C) $P(X \ge 301)=1 - P(X \le 301)$ [/tex]

D) $P(260 \le X \le 280) = ...$

You said it is a normal distribution; so

$P(X \le t) = \frac{1}{\sqrt{ 2\pi \sigma^2}} \int^t_{-\infty}e^{(-s-\mu)^2 / (2\sigma^2)} dx$

$\mu$ = mean

$\sigma$ = standard deviation

Well, I must admit, I have absolutely no clue, if this is okay or not; but it seemed to bevery important for you

Quote:

i really need help on these problems !

Rapha
May 19th 2009, 12:16 AM
chobozor

Thank you i will give that a try, yea i have a test on it tommorrow =(