Solution:

Class interval      Frequency           Cumulative recurrence

15-20     2             2

20-25     4             6

25-30     18           24

30-35     21           45

35-40     33           78

40-45     11           89

45-50     3             92

50-55     6             98

55-60     2             100

Given information: n = 100 and n/2 = 50

Middle class = 35-45

Then, at that point, l = 35, cf = 45, f = 33 and h = 5

\[\begin{array}{*{35}{l}}

   Middle\text{ }=\text{ }35+\left( \left( 50-45 \right)/33 \right)\text{ }\times \text{ }5  \\

   ~  \\

   =\text{ }35\text{ }+\text{ }\left( 5/33 \right)5  \\

   ~  \\

   =\text{ }35.75  \\

\end{array}\] Thusly, the middle age = 35.75 years.