Compute the critical value Za2 that corresponds to a 80 leve

Compute the critical value Za/2 that corresponds to a 80% level of confidence.

Solution

To find z-score for 80% you will need the table of Standard Normal Probabilities (Table A).

80% = 0.8000 which represents the middle area under the normal curve.

(1 ? 0.8000) / 2 = 0.1000 which is one of the two tail areas.

Since Table A contains left-tailed areas, we can use the number 0.1000 to find the z-score corresponding to it to be ? 1.28.

Now, what you need the z-score for the right-tailed area. Since, both tails have equal area, the z-score for the right-tailed area is equal to 1.28 (we ignore the \"?\" sign).

Answer: z = 1.28