Final answer:
The z-score for α=0.21 can be found using a standard normal distribution table or a statistical calculator, and it is approximately in the range between the z-scores for α=0.20 and α=0.25.
Step-by-step explanation:
The student is asking for the z-score corresponding to an alpha level (α) of 0.21 in the context of a standard normal distribution. The z-score, often denoted as zα, is a statistical measurement that represents the number of standard deviations an element is from the mean of the distribution. In statistical tables, the z-score is commonly associated with the cumulative probability to the left of the z-score in a standard normal distribution.
To find the value of z0.21, one would typically use a standard normal distribution table or a calculator's statistical functions. Based on the reference information provided, finding an exact match for α=0.21 is not possible. However, we can approximate that since the value of z for an alpha level of 0.2 is not listed, it will be close to the z-score just above or below this alpha level.
Without the exact value in the provided references, the standard procedure would be to refer to a z-score table or use computational tools to determine that the z-score for α=0.21 lies between the value for α=0.2 and α=0.25 based on typical z-score tables or statistical software. As an approximation, we can suggest it's in the vicinity of the provided z-scores for those alpha levels.