Statistics - Important Points
CBSE Class 9 - Mathematics
① In statistics we study collection, presentation analysis and interpretation of data.② Facts or figures collected with a definite purpose are called data.
③ Data are fundamental. Statistical tests are performed on raw not manipulated data.
④ The number of times an observation occurs in the given data is called frequency of the observation.
⑤ Class intervals are the groups in which all observations are divided.
⑥ For class interval 40-50, 50 is called upper class limit and 40 is called lower class limit.
⑦ Data arranged in ascending or descending order is called arrayed data.
x Class mark = | Lower Class Limit + Upper Class Limit |
2 |
⑨ The three measures of central tendency for an ungrouped data are: - Mean - Median - Mode
⑩
x Average Mean = | Sum of all observations |
Number Of Observations |
⑪ For raw data mean,
x Mean,x = | Σx_{i} |
n |
Σx_{i} means 'the sum of all valúes of x'.
⑫ When frequency fi is given.
x Mean,x = | Σx_{i}f_{i} |
Σf_{i} |
⑬ Mode is the value of observation which occurs most frequently.
⑭ The median is the middle value. There is an equal number of values above and below it.
⑮ For median arrange the data in ascending order or descending orders.
⑯ If number of observations ‘n’ is odd, median is
x Median = | (n+1)^{th} term |
2 |
⑰ If number of observations ‘n’ is even
x Median = | ½(n)^{th} term + ½(n+1)^{th} term |
2 |
⑱ Empirical formula for calculating mode is given by, Mode = 3 (Median) – 2 (Mean)
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