Final answer:
The z-score for a 91% confidence interval is approximately 1.70, found by looking for a z-value that leaves 95.5% of the distribution to its left in standard normal distribution tables.
Step-by-step explanation:
The z-score that corresponds with a 91% confidence interval is not typically standard, as common confidence levels are 90%, 95%, and 99%. However, to find the z-score for a 91% confidence interval, we need to consider the fact that such an interval would leave 9% in the tails of the normal distribution, meaning 4.5% in each tail since the normal distribution is symmetric. Consulting a z-table or using a statistical software, one needs to find the z-value that leaves 0.955 (1 - 0.045) to the left of it. This z-score is approximately 1.70. Remember that these values can vary slightly depending on the z-table or software used.
The z-score that goes with a 91% confidence interval is approximately 1.695. The critical value for a 91% confidence interval corresponds to the area of 0.045 in the far left tail and 0.045 in the far right tail of a standard normal distribution. This value can be found using a z-table or a calculator function like ZInterval. The z-score represents the number of standard deviations above or below the mean that corresponds to a given level of confidence.