Question

find the value of 11 + 13 + 15 +___+ 99​

Answer 1

Answer:

here the 1st term a=11

common difference d=(13-11)=2

let 99 is the nth term

99=11+(n-1).2

=> 99-11=(n-1).2

=> 88=(n-1).2

=> n-1=88/2=44

=> n=44+1=45

so ,

11+13+15+...

=45/2{2.11+(45-1).2}

=45/2(22+88)

=45/2.110

=45×55

=2475