Preparing a cumulative frequency table from the given data, we get.
Class (X) | Frequency(F) | Cumulative frequency (C.F) |
0 - 5 | 2 | 2 |
5 - 10 | 4 | 6 |
10 - 15 | 14 | 20 |
15 - 20 | 15 | 35 |
20 - 25 | 6 | 41 |
25 - 30 | 4 | 45 |
N = 45 |
By formula,
First quartile (Q1) = The value of \((\frac N4)^{th}\) item
=The value of \((\frac{45}4)^{th}\) item
= The value of 11.25th item.
Here, C.F just greater than 11.25 is 20 and it lies in the class (10 - 15).
Therefore, First quartile class = (10 - 15)
Again, by formula
First quartile (Q1) = \(L\;+\;(\frac{{\displaystyle\frac N4}-c.f}f)\times i\)
Where, L = 10, \(\frac N4\) = 11.25, c.f = 6, f = 14, i = 5
Therefore, Q1 = 10 + \(10\;+\;(\frac{11.25\;-\;6}{14})\times5\)
= \(10+\frac{5.25}{14}\times5\)
= 10 + 1.88
First quartile (Q1) = 11.88