## Statistics - Important Points

CBSE Class 9 - Mathematics
In statistics we study collection, presentation analysis and interpretation of data.

Facts or figures collected with a definite purpose are called data.

Data are fundamental. Statistical tests are performed on raw not manipulated data.

The number of times an observation occurs in the given data is called frequency of the observation.

Class intervals are the groups in which all observations are divided.

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

The three measures of central tendency for an ungrouped data are: - Mean - Median - Mode

 x Average Mean = Sum of all observations Number Of Observations

For raw data mean,
 x Mean,x = Σxi n

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

When frequency fi is given.
 x Mean,x = Σxifi Σfi

Mode is the value of observation which occurs most frequently.

The median is the middle value. There is an equal number of values above and below it.

For median arrange the data in ascending order or descending orders.

If number of observations ‘n’ is odd, median is
 x Median = (n+1)th term 2

If number of observations ‘n’ is even

 x Median = ½(n)th term + ½(n+1)th term 2

Empirical formula for calculating mode is given by, Mode = 3 (Median) – 2 (Mean)  