Sum of n terms of A.P

s40={41,42,....80}

so sum of all terms in s40

=41+42+..+80

this is the sum of an A.P.

 with 41 as the first term(a) and 1 as the common diff.(d) and there are total 40 terms(n)

so using the formula

sum of n terms

=n/2[a+l} where l is the last term

we get

reqd sum

=40/2[41+80]

=4840