To pick out the middle 20 percent of a normal distribution, which two percentiles do you need?

1. The middle 20 percent leaves 80 percent outside it. 2. That 80 percent splits evenly between the two tails. 3. So each tail carries an area of 0.40. 4. The lower cut has 0.40 below it, which is the 40th percentile. 5. The upper cut has 0.40 plus 0.20, or 0.60, below it, which is the 60th percentile. 6. So the two cuts are the 40th and the 60th percentiles. 7. The 20th and 80th would trap the middle 60 percent instead. 8. The 25th and 75th would trap the middle 50 percent, the interquartile range. 9. The 10th and 30th sit both below the centre and trap no middle band at all. _Source: OpenStax High School Statistics (CC BY 4.0), Ch 6 "The Normal Distribution", section 6.2 Using the Normal Distribution_