First term f = 1
If first four terms are f, f + d, f + 2d, f + 3d
f + f + d + f + 2d + f + 3d = 100
4f + 6d = 100 (divided by 2 , both sides )
2f + 3d = 50
2 + 3d = 50
3d = 50 – 2
3d = 48
d = 48/3
d = 16
The arithmetic sequence is 1, 17, 33, 49, ………….