# Question on Determing the Proportion

• May 18th 2009, 11:11 PM
chobozor
Question on Determing the Proportion

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 $\displaystyle P(X \le 244)$

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

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

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

You said it is a normal distribution; so

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

$\displaystyle \mu$ = mean

$\displaystyle \sigma$ = 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 =(