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Finding z critical values for Confidence Interval

Since we use the left cumulative z-table, we need to find the left-tailed area to find the negative z-critical value.

First, subtract the given confidence level from one and then divide it by 2 to get the left area.

Look up the table using the left area to find one of the critical values.

Once we get the negative critical value, then make it positive to have another one.