Answer 1

120, 60, 30, 18, …

r = `("t"_2)/("t"_1) = ("t"_3)/("t"_2) = ("t"_4)/("t"_3)`

Here r is not equal i.e. `60/120 = 30/60 ≠ 18/30`

∴ It is not a G.P.