Given sequence is 3,8,13,.....373.
Here a=3,d=5andan=373
Now an=a+(n−1)d
⇒373=3+(n−1)5
⇒n=75
We know that Sn=2n(a+an)
⇒S75=275(3+373)
⇒S75=14100
Now let us write the sequence of terms which are divisible by 3.
We get, 3,18,33,.....363
⇒363=3+(n−1)15
⇒n=25
Now let us find the sum of terms divisible by 3.
⇒Sdivby3=225(3+363)=4575
Required sum =Sum of 75 terms−Sum of terms divisible by 3
=14100−4575
=9525.
Therefore, the required sum is 9525