If the sum of first 7 terms and 15 terms of an a.p are `98 and 390` respectively then find the sum of first 10 terms​

If the third and 11th terms of an A.P. are 8 and 20 respectively, find the sum of first ten terms.

If the second term and the fourth terms of an A.P. are 12 and 20 respectively, then find the sum of first 25 terms:

The sum of first 10 terms and 20 terms of an AP are 120 and 440 respectively. What is its first term ?

If the second and seventh terms of an A.P. are 2 and 22 respectively. Find the sum of first 35 terms:

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

If sum of first 6 terms of an AP is 36 and that of the first 16 terms is 256 , then find the sum of first 10 terms.

The 1st term and the common difference of an A.P. are 10,000 and 2000 respectively . Find the sum of the first 12 terms.

The sum of first p- terms terms of an A.P.is q and the sum of first q terms is p,find the sum of first (p+q)

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