[" 17.In an "1P" .If a "=1," an "=20" and "Sn=399," then "n" is "],[[" 17.In "19," b) "21," c) "38]]

In an AP, if a = 1 , a_(n)= 20 and S_(n) = 399 , then n is equal to

In an AP, if a = 1 , a_(n)= 20 and S_(n) = 399 , then n is equal to

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

S_n in A.P.=

If t_n=sum_1^n n , find S_n=sum_1^n t_n .

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

In an A.P, 1st term is 1 and the last term is 20 .The sum of all terms is 399 , then n=…. a) 42 b) 38 c) 21 d) 19

In an A.P. third term is 14 and 8th term is 34. Find S_n and S_(20) .