In an A.P., if a = 1, an = 20 and Sn = 399, then n is

In an A.P., if a = 1, a_n = 20 and S_n = 399, then n is
(a) 19
(b) 21
(c) 38
(d) 42

Solution:

In an A.P., if a = -5, l = 21. and S_n = 200, then n is equal to
(a) 50
(b) 40
(c) 32
(d) 25

Solution:

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