Question

In a test, the marks obtained by 100 students (out of 50) are given below: 

Marks obtained:	0 – 10	10 – 20	20 – 30	30 – 40	40 – 50
Number of students:	12	23	34	25	6

Find the mean marks of the students. 

Answer 1

Marks obtained	Number of Students  `f_i`	`x_i`	`x_i − 25`	`u_i f_i`
0 – 10	12	5	−20	−240
10 – 20	23	15	−10	−230
20 – 30	34	25	0	0
30 – 40	25	35	10	250
40 – 50	6	45	20	120
	100			−100

Let assumed mean = 25

`u_i = x_i - 25`

Short cut method

`barx = a + sum(u_i f_i)/f_i`

= `25 + ((-100))/100`

= 25 - 1

`barx = 24`