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

The sum of first 8 terms and first 24 terms of an A.P. are equal. Find the sum of its 32 terms.

The sum of first 8 terms and first 24 terms of an A.P. are equal. Find the sum of its 32 terms.

Find the sum of first n terms of an AP whose n^(th) term is 5-6n .find the sum of its first 20 terms

The sum of first P terms of an A.P. is equal to the sum of its first Q terms. Show that the sum of its first (P+Q) terms is zero.

The sum of first 8 terms of an A.P. is 64 and that of first 15 terms is 225. Find the sum of its first 17 terms.

The sum of first 8 terms of an A.P. is 64 and that of first 15 terms is 225. Find the sum of its first 17 terms.

The sum of the first 8 terms of an A.P. is 100 and the sum of its first 19 terms is 551. Find the first term and the common difference of the AP.

If the sum of the first 9 terms of an AP is equal to the sum of its first 11 terms, then find the sum of its first 20 terms.