Caculate mode of the following data :
`{:("Marks",0-5,5-10,10-20,20-40,40-60,60-80,80-90,90-100),("Number of Students"," "5," "7," "9," "25" "," "30," "24," "8," "6):}`

Explanation

This is a series with unequal class intervals . Calculation of mode requires that this series be converted into one with equal class interval of 20 , as shown below :
`##TRJ_ECO_XI_C01_S01_021_S01.png" width="80%">
A glance at the table reveals that 40-60 is the model class . the actual value of mode is ,
`Z=l_(1)+(f_(1)-f_(0))/(2f_(1)-f_(0)-f_(2))xxi`
`=40+(30-25)/(2(30)-25-24)xx20`
`=40+(5)/(60-49)xx20`
`=40+(5)/(11)xx20=40+9.09=49.09`
Mode (Z) = 49.09.