defence exam Agniveer Vayu Group X & XY Mock Test 01/2026 Mathematics Sequences and Series Geometric Progressions
If each term of a geometric progression a1, a2, a3 ,… with a1 = \(\frac{1}{8}\) and a2 ≠ a1, is the arithmetic mean of the next two terms and Sn = a1 + a2 + … + an, then S20 – S18 is equal to
1
215
2
-218
3
218
4
-215