The following table shows the marks obtained by 100 students of class X in a school during a particular academic session. Find the mode of this distribution.

Marks No. of students

Less than 10 7

Less than 20 21

Less than 30 34

Less than 40 46

Less than 50 66

Less than 60 77

Less than 70 92

Less than 80 100

 Marks No. of students

Less than 10 7

Less than 20 21

Less than 30 34

Less than 40 46

Less than 50 66

Less than 60 77

Less than 70 92

Less than 80 100

Marks No. of students

00 - 10 = 7

10 - 20 = 21 - 7

20 - 30 = 34 - 21

30 - 40 = 46 - 34

40 - 50 = 66 - 46

50 - 60 = 77 - 66

60 - 70 = 92 - 77

70 - 80 = 100 - 92

Marks No. of students

00 - 10 = 7 

10 - 20 = 14

20 - 30 = 13

30 - 40 = 12

40 - 50 = 20 MODAL CLASS ( most frequency )

50 - 60 = 11

60 - 70 = 15

70 - 80 = 8

Mode = l + (f - f1) / 2f - f1 - f2 * h

l = 40

f = 20

f1 = 12

f2 = 11

h = 10

Mode = 40 + (20 - 12) / 2*20 - 12 - 11  * 10

=> 20 + 8 / 40 - 23 * 10

=> 20 + 8 / 17 * 10

=> 20 + 0.47 * 10 

=> 20 + 4.7

=> 24.7 ( approx.... )