The sum of an A.P. is 1 and the `nth` term is 20. If `S_(n)=399`, then `n=…..`

Choose the correct alternative answer: The first term of an A.P. is 1 and nth term is 20 . If S_n=399 , then n=?

The first term of an A.P. is 1 and nth term is 25 If S_(n)=520 , then n = ….

Choose the correct alternative: The first term of an A.P. is 1 and nth term is 25 . If S_n=520 , then n=….

The first term of an A.P. is 2 and the nth term is 29 . If S_(n) = 465 , then what is the value of n ?

The first term of an A.P. is 2 and the nth term is 41. What is the value of n, if S_(n) = 860 ?

The nth term of an A.P. is (1)/(n) and nth term is (1)/(m). Its (mn)th term is :

The mth term of an A.P. is n and nth term is m. Then rth term of it is

In an A.P., if a = 1 , a_(n) = 20 and S_(n) = 399 , then n = ……..

Find the sum of an A.P. of :- 26 terms whose nth term is (2n + 1)/3 .

Find the sum of an A.P. of :- 26 terms whose nth term is 2n + 5.