Confidence intervals

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What is the value of za/2 for an 80% confidence interval?
a. .255.
b. 1.28.
c. .0398.
d. .525.

i know the answer is a, but does anyone know how to calculate that :blushing: ?
 

Answers and Replies

  • #2
HallsofIvy
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Agent_J said:
What is the value of za/2 for an 80% confidence interval?
a. .255.
b. 1.28.
c. .0398.
d. .525.

i know the answer is a, but does anyone know how to calculate that :blushing: ?
Not in any easy manner- you look it up in a table!
Here's one on the internet:
http://people.hofstra.edu/faculty/Stefan_Waner/RealWorld/normaltable.html [Broken]
 
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