Question

the middle term of arithmetic series consist of 25 terms is 20. find the sum of the series

Answer 1

Since there are 25 terms which is odd
so, the middle term is (25+1)/2 th term
that is 13th term
atq,13th term =20
=>a+12d=20. ......1
sum of the series=n/2{2a+(n-1)d}
=25/2{2a+(25-1)d}
=25/2{2a+24d}
taking 2 as common
=25/2{2(a+12d)}
=25(a+12d)
from 1,a+12d=20
=25x20=500(ans)

Answer 2

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