# Z problem

• Dec 1st 2008, 10:46 AM
ndcruz
Z problem
I calculated my z value to be z=(23-18)/3 = 5/3 = 1.66

I am trying to find P(Z>1.6666) = ?

can someone please explain how to get this probability using the Z table?

i got 0.0485

0.5 - 0.4515
• Dec 1st 2008, 11:01 AM
Moo
Hello,
Quote:

Originally Posted by ndcruz
I calculated my z value to be z=(23-18)/3 = 5/3 = 1.66

I am trying to find P(Z>1.6666) = ?

can someone please explain how to get this probability using the Z table?

i got 0.0485

0.5 - 0.4515

Well, if this is what you got by using the Z table, then you know how to use it, because your answer is correct... :p

The z table represents the area bounded by the Gaussian curve, the x axis, the y axis and the line x=a, where a is the z value of the table.

So in fact, tables give you this probability : \$\displaystyle P(0<z<a)\$

Let a>0 and b<0. Let \$\displaystyle z_a\$ and \$\displaystyle z_b\$ be the z scores of a and b.
\$\displaystyle P(z<a)=0.5+z_a\$
\$\displaystyle P(z>a)=0.5-z_a\$
\$\displaystyle P(z>b)=0.5+z_b\$
\$\displaystyle P(z<b)=0.5-z_b\$