Question

Find the sum of arithmetic sequence which contains 25 terms and whose middle term is 20​

Answer 1

SOLUTION ☺️

25 terms which is odd terms

so, the middle term = (n+1)/2th term

=) 25+1/2

=) 26/2

=) 13th term

A/q

=) 13th term= 20term

=) a+12d= 20..........(1)

Sum of the series= n/2[2a+(n-1)d]

=) 25/2[2a+(25-1)d]

=) 25/2×2[a+12d]

=) 25[a+12d]

=) 25(20)......(using Equation 1)

=) 25×20

=) 500

HOPE it helps ✔️