The median (the middle value in a set that has been ordered lowest to highest) is the value above which half of the remaining values fall and below which the other half of the remaining values fall. Because there is an even number of scores in our example (20), the median score is the average of the two middle scores (10th and 11th)—580 and 600—or 590.The lower quartile ( Q1or 25th percentile) is the median of the bottom half. The bottom half of this set consists of the first ten numbers (ordered from low to high): 280, 340, 440, 490, 520, 540, 560, 560, 580, and 580. The median of those ten is the average of the fifth and sixth scores—520 and 540—or 530. The lower-quartile score is 530. The upper quartile ( Q3or 75th percentile) is the median score of the top half. The top half of this set consists of the last ten numbers: 600, 610, 630, 650, 660, 680, 710, 730, 740, and 740. The median
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