# Math Help - Measures of dispersion problem

1. ## Measures of dispersion problem

marks number of student
10-19 2
20-29 8
30-39 x
40-49 13
50-59 5

a)given that the first quartile mark is 30.5.Find the value of $x$

b)find the total number of students.

2. ## First Quartile

The first quartile is the point below which 25% of the cases fall and above which 75% of the cases fall

10-19 2
20-29 8
30-39 x
40-49 13
50-59 5

x+13+5 = (2+8)3
x+18 = (10)3
x+18 = 30
x = 12