find (i) arithmetic mean (ii) median (iii) mode of following data . marks obtained by 20 student

78,19, 25, 18, 18, 25, 28, 73, 80, 55, 9, 85, 80, 92 ,15 ,23, 90, 65, 55, 45.

let us arrange the data in ascending order:

9 , 15, 18, 18, 19, 23, 25, 25, 28, 45, 55, 55, 65, 73, 78, 80, 80, 85, 90, 92

arithmetic mean = sum of the observations / number of observations

since the number of observations are 20.

therefore it has two mid-terms, 10th term and 11th term.

10th term = 45, 

11th term = 55

median = average of the mid-terms

mode  is the value that occurs most often.

it has more than one mode.

mode of the above data = 18, 25, 55, 80

hope this helps you.

cheers!!