Step 1: Recall the formula of the median for grouped data.

Median = l + \frac{\frac{n}{2} + cf}{f} * h

where, l = lower boundary of median class,

n = number of observations,

cf = cumulative frequency of class preceding the median class,

f = frequency of median class,

h = class size (size of the median class).

Step 2: Set up a cumulative frequency distribution table

NOTE: The cumulative frequency is calculated using a frequency

distribution table.

Step 3: Calculate the median class of the data.

NOTE: Locate the class whose cumulative frequency exceeds

\frac{n}{2} for the first time. This is called the median class.

The total number of observations n = 100

\frac{n}{2}=\frac{100}{2}

125 - 145 is the class whose cumulative frequency is 86 greater than

(and nearest to) \frac{n}{2}, i.e., 50.

Therefore, 35 - 45 is the median class

Step 4: Substitute that values in the median formula

From the table;

l = lower boundary of median class = 35,

n = number of observations = 100,

cf = cumulative frequency of class preceding the median class = 45

f = frequency of median class = 33

h = class size (size of the median class) = 20 - 15 = 5.

Substituting the values

Median = l + \frac{\frac{n}{2}-cf}{f}*h

Median = 35 + \frac{50 - 45 }{33}*5

= 35 + \frac{25}{33}

= 35 + 0.75

Hence, the median = 35.75