There is no exact match for 0.8000 and the closest is 0.7995, which produces the z-score of. If you look up the area 0.8000 in a standard normal table, the corresponding z-score is. Either use software or a standard normal table. ![]() The 80th percentile (Figure 2) is the area of a left tail that excludes 20% of the area on the right.įinding the 80th percentile (or for that matter any other percentile) is easy. The middle 80% under a bell curve (Figure 1) is the middle section of the bell curve that exlcudes the 10% of the area on the left and 10% of the area on the right. The following figures show the difference between the middle 80% under a bell curve and the 80th percentile of a bell curve. The question in the email is a teachable moment and deserves a small blog post. The student sent me an email asking for an explanation. ![]() The student then tried to answer the practice problem with the 80th percentile, which of course, did not match the answer key. The student was confusing the middle 80% of a bell curve with the 80th percentile. A student sent me an email about a practice problem involving finding the middle 80% of a normal distribution.
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