Question

find the middle term of the series 15,21,27........,135

Answer 1

72 is the answer of your question.

Because

15+21+27 - 135
63 - 135
= 72.

HOPE THIS HELPS YOU.

REGARDS
MONICA.

Answer 2

Tn=135,d=21-15=6,a=15
Tn =135
a+(n-1)d=135
15+(n-1)6=135
15+6n-6=135
6n+9=135
6n=135-9
6n=126
n=21
Middle term =n+1/2
=21+1/2
=22/2
=11