Question

The first term and the common difference of an A.P. is 10 and 5 respectively. Complete the following activity to find the sum of first 30 terms of the A. P.  

`S_n=n/2[ ____+(n-1)d ]`

`∴ s_30=30/2[20+(30-1)xx _____ ]`

=`15[20+________]`

=`15xx165`

=_________ 

 

Answer 1

`S_n=n/2[2a+(n-1)d]` 

`∴ S_30=30/2[20+(30-1)xx5]` 

=` 15[20+145]` 

=`15xx165`

=`2475`