Which of the following series is not in the geometrical series?

Option 2 : 12, 24, 36, ...

Concept used:

A Geometric Series is a progression of numbers with a constant ratio between each number and the one before (e.g. 1, 3, 9, 27, 81).

Calculation:

Option 1:

5, 15, 45, ...

15 = 5 × 3

45 = 5 × 3²

So, it's a Geometric Series.

Option 2:

12, 24, 36, ...

24 = 12 × 2

36 = 12 × 3

So, it's not a Geometric Series.

Since we've already encountered an option that doesn't follow the Geometric series pattern, we aren't required to check any further.

∴ 12, 24, 36, ...  of the following series is not in the geometrical series.