The heart of 60 patients were examined through X-ray and the observations obtained are given below :

Diameter of heart (in mm)	Number of patients
120	7
121	9
122	15
123	12
124	6
125	11

Find the median.

Cumulative frequency table :

Total number of observations = 60, which is even.

By formula,

$\Rightarrow \text{Median} = \dfrac{\left(\dfrac{n}{2}\right)^{\text{th}} \text{term} + \left(\dfrac{n}{2} + 1\right)^{\text{th}} \text{term}}{2} \\[1em] \Rightarrow \text{Median} = \dfrac{\left(\dfrac{60}{2}\right)^{\text{th}} \text{term} + \left(\dfrac{60}{2} + 1\right)^{\text{th}} \text{term}}{2} \\[1em] \Rightarrow \text{Median} = \dfrac{\text{30th term} + \text{31st term}}{2} \\[1em] \Rightarrow \text{Median} = \dfrac{\text{122} + \text{122}}{2} \\[1em] \Rightarrow \text{Median} = \dfrac{\text{244}}{2} \\[1em]$

∴ Median = 122.

Hence, median = 122 mm.