In an A.P. if a = 1, an = 20 and Sn = 399, then n is
19
21
38
42
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If the first term of an A.P. is -5 and the common difference is 2, then the sum of its first 6 terms is
0
5
6
15
In an A.P., if a = -5, l = 21 and S = 200, then n is equal to
50
40
32
25
The sum of first five multiples of 3 is
45
55
65
75