Math Is Fun Forum

ninjaman

Member

Registered: 2013-10-15

Posts: 61

normal distribution, find percentage

hello

I have a question

the lengths of pins produced by a machine follow a normal distribution with mean 2.54cm and standard deviation 0.04cm. a pin is rejected if the length is less than 2.44cm or more than 2.60cm

A/ find the percentage of pins that are accepted.

B/ if it is decided that 2.5% of the pins are to be rejected because they are too long and 2.5% because they are too short, determine the new range of acceptable lengths.

for the first part I have the formula, z = x-MU / sigma, I rearranged this

sigma is 0.04cm
MU is 2.54cm

so I used this z * sigma + MU = x, z * 2.58 = ? so here I thought I would take a value from a table and divide by 2.58 until I got an accurate z value. then use that z for the rest.
if anyone could confirm this method as im not to sure? the rest I think I can get.

thanks
simon

ShivamS

Member

Registered: 2011-02-07

Posts: 3,648

Re: normal distribution, find percentage

Hi;

this problem was posted here a while back.
http://www.mathisfunforum.com/viewtopic.php?id=16730