� The second-order differential equation �dv

� �av

� bx � dt � �dx

� v �� dt

2 d x dx � a � bx � 0 can be expressed as

2 dt dt

� Relationship between frequencies and cumulative frequencies : Data

Frequency

Data less than or equal to

Cumulative frequency

� Measures of central tendency for a data set { x1 , x2, x3, , x } arranged in ascending order : x1 � x2 � x3 � � xn 1 . x �

: Mean n 2 . The datum or the average value of two data at the middle : Median 3 . The datum appears the most : Mode

� Measures of dispersion for a data set { x1 , x2, x3, , x } arranged in ascending order :

1 . xn � x1

: Range

2 . Two subgroups A and B can be formed from the data set such that all data of the subgroup A are less than or equal to the median , while all

data of the subgroup B are greater than or equal to the median 3 . Q1

� The median of the subgroup A : Lower quartile

4 . Q3

� The median of the subgroup B : Upper quartile 5 . Q3� Q1: Inter-quartile range ( IQR )

n n

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