Final answer:
The percentage of the distribution in the rejection region of one tail for a two-tailed test with an alpha of .05 is 2.5%. This is because the 5% alpha level is split between the two tails of the distribution.
Step-by-step explanation:
For a two-tailed test with an alpha of .05, the percentage of the distribution that is in the rejection region of one tail is 2.5%. This is because the total area under the curve representing the alpha value is split equally between the two tails of the distribution. Therefore, since alpha is 0.05, each tail will contain half of this, which is 0.025 or 2.5%. Thus, when constructing a two-sided 95 percent confidence interval, 2.5 percent of the probability will be in each tail of the normal distribution. In the context of hypothesis testing, if the p-value is less than the alpha level of significance (in this case, 0.025 for each tail), we would reject the null hypothesis. This is a fundamental concept in statistics as it defines the acceptance range for test results within the distribution under the null hypothesis.