confidence level of 80% what does that transcribe to? e.g. 90% confidence level is = Za/2 of 1.960

The makers of a soft drink want to identify the average age of its consumers. A sample of 16 consumers is taken. The average age in the sample was 22.5years with a standard deviation of 5 years.
construct a 95% confidence level

22.5+  1.96 5/ square root of 16 = 1.96 x 5/4 = 1.96 x 1.25 = 2.45

now do the same thing with 80 % confidence level.
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