# Thread: finding a proportion ........

1. ## finding a proportion ........

I would like to get some help in finding a proportion considering that :
mean = 70 inches
standard deviation = 2.8 inches

What proportion of men are less than 68 inches tall? By the way , does someone can tell me what to do in order to do this problem with a ti-84/83 using the function called normalcdf ? Because I don't want to use the standard normal table . Thanks in advance.

2. Originally Posted by skorpiox
I would like to get some help in finding a proportion considering that :
mean = 70 inches
standard deviation = 2.8 inches

What proportion of men are less than 68 inches tall? By the way , does someone can tell me what to do in order to do this problem with a ti-84/83 using the function called normalcdf ? Because I don't want to use the standard normal table . Thanks in advance.
Calculate Pr(X < 68).

Your calculator manual (also available on-line from the TI homepage, follow the links) will outline how to use your calculator. You will need to use -1E99 as good approximation to -oo in this context.

3. The answer is .2389 ; however , whenever I try on my calculator , I obtain .23753. The procedure I use is normalcdf(-1 e 99, 68, 70 , 2.8) , and I'm not sure whether that's ok or not. Anyway , thanks for your time Mr. Fantastic.

4. Originally Posted by skorpiox
The answer is .2389 ; however , whenever I try on my calculator , I obtain .23753. The procedure I use is normalcdf(-1 e 99, 68, 70 , 2.8) , and I'm not sure whether that's ok or not. Anyway , thanks for your time Mr. Fantastic.
0.23753 is correct (to five decimal places).

0.2389 has probably been got using tables (which are not as accurate as technology).