CBSE Class 9 - Mathematics - CH 14: Statistics - Important Points

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.

⑧

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 =	Σxi
	n

Σx_i means 'the sum of all valúes of x'.

⑫ When frequency fi is given.

x Mean,x =	Σxifi
	Σfi

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)