UPSC Prelims 2025 CSAT, question 36

Solution.

Answer: (b) 12

1. Look at the ratios of consecutive terms from the third term onward: $\frac{18}{12} = 1.5$, $\frac{36}{18} = 2.0$, and $\frac{90}{36} = 2.5$.
2. The multipliers increase by $0.5$ at each step ($\times 0.5, \times 1.0, \times 1.5, \times 2.0, \times 2.5$), so $X = 24 \times 0.5 = 12$ (and $12 \times 1.0 = 12$).