# Math Help - Normal Distrbution , how to find sign of z

1. ## Normal Distrbution , how to find sign of z

In a normal Distribution 31% of the item are under 45 and 8 % are above 64.Find its mean and SD?
In a normal Distribution 31% of the item are under 45 and 8 % are above 64.Find its mean and SD
My doubt is how to know if z < 0 or >0 .
I really need to understand the concept behind taking z1. What does 31 % indicate? negative as it is below 50 % ? Somebody please help me.I'm badly in need of a way to solve this problem

2. ## Re: Normal Distrbution , how to find sign of z

Originally Posted by jeevanbmanoj
In a normal Distribution 31% of the item are under 45 and 8 % are above 64.Find its mean and SD?
In a normal Distribution 31% of the item are under 45 and 8 % are above 64.Find its mean and SD
My doubt is how to know if z < 0 or >0 .
I really need to understand the concept behind taking z1. What does 31 % indicate? negative as it is below 50 % ? Somebody please help me.I'm badly in need of a way to solve this problem
Pr(Z < 0) = 0.5. 31% is equivalent to a probability of 0.31. So what does that tell you about the z-value corresponding to 45 ....?

Pr(Z > 0) = 0.5. So what does that tell you about the z-value corresponding to 64 ....?