The nth term of a series is 9- 5n. Is this C grade? If yes, then find the sum of the first 15 terms...

If the sum of the first n terms of the series

If the sum of the first 9 terms of an A.P. is 81 and that of the first 18 terms is 324, find the sum of its first n terms.

The nth term of a series is 3^(n)+2n; find the sum of first n terms of the series.

If the sum of first 10 terms of an A.P is 60 and sum of first 15 terms is -165 then find the sum of its n terms

The sum of first three terms of a G.P. is 15 and sum of next three terms is 120. Find the sum of first n terms.

The 5^(th) term of an AP is 50. Find the sum of first 9 terms.

Find the sum of first n terms of an AP whose nth term is (5n-1). Hence,find the sum of first 20 terms.

The sum of n terms of a series is 3n^2+5n find the value of n if nth term is 152:

The sum of first 5 terms and first 15 terms of an A.P. are equal. Find the sum of its first 20 terms.