Determing Z score from level of confidence

#1
How can I determine the Z score, given a level of confidence of 65%. My math book has the z score for .80, .90, .95, and .99 but none other.

Like for .90, it gives a zscore of 1.645. I tried to look in the table and see how 1.645 matches up to .90, but I see no correlation. Is there some equation I need to use?


My problem gives me the following

level of confidence= .65 sample stan deviation= 2.5 sample size = 36

It asks me to find the margin of error.
So I simply need to find the corresponding zscore for the level of confidence .65 and multiply it by the stan dev / square root of the sample size
 
Last edited:

JohnM

TS Contributor
#2
You can use the z table (normal distribution table) in your textbook, or you can also use Excel, which has a bunch of stats functions, including determining a z score from a probability, and vice-versa.