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## Main Question or Discussion Point

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 ?

a. .255.

b. 1.28.

c. .0398.

d. .525.

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