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Quartile

Symbol	Names	Definition
Q1	first quartile lower quartile 25th percentile	splits off the lowest 25% of data from the highest 75% 일사분위수 (하한사분위수)
Q2	second quartile median 50th percentile	cuts data set in half (중앙값)
Q3	third quartile upper quartile 75th percentile	splits off the highest 25% of data from the lowest 75% 삼사분위수 (상한사분위수)

interquartile and outliers

사분범위 = Q3 - Q1
사분범위 = (상한사분위수) - (하한사분위수)

> duration = faithful$eruptions     # the eruption duration
> quantile(duration)                # apply the quantile function 
    0%    25%    50%    75%   100% 
1.6000 2.1627 4.0000 4.4543 5.1000

quantile, not qurtile