Find the sum of first twenty terms of Arithmetic series 2 +7+12 + `cdots ` using suitable formula.

Find the sum of the first 28 terms of the series.

Find the sum of n terms of the series 1 + 4/5 + 7//5^(2) + 10//5^(3)+ cdots

Find the sum of n terms of the series : 5+7 +13 +31+85 + cdots .

Find the sum to n terms of the series 4+41+401+4001+ cdots

Find the sum to n terms of the series 4+44+444+4444+ cdots

Find the sum to n terms of the series 3+15+35+63+ cdots .

Find the sum of first 35 terms of the series whose pth term is (p)/(7)+2

Write the formula to find the sum of first n terms of an Arithmetic progression, whose first term is a and the last term is a_n .

Write the formula to find the sum of first n terms of an Arithmetic progression, whose first term is a and the last term is a_n .

Find the sum of first 20 terms of the arithmetic progression having the sum of first 10 terms as 52 and the sum of the first 15 terms as 77.