What value of z a2 in the CI formula 75 results in a confide

What value of z a/2 in the CI formula (7.5) results in a confidence level of 99.7%?

Solution

1.

As

alpha/2 = [1 - confidence level]/2 = 0.0015

Using technology or table to get z(alpha/2),

z(alpha/2) = 2.9677 [ANSWER]

In Excel, you can type on any empty cell

=NORMSINV(0.0015)

and it will display -2.9677. We want the absolute value, so we disregard the sign.

You can also use a normal distribution table.

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