Find X in sequence 24,X,12,18,36,90

Analyze the ratio between consecutive terms to uncover the sequence pattern. Let's check the known consecutive terms: 12 × 1.5 = 18, 18 × 2 = 36, and 36 × 2.5 = 90. This strongly suggests an incremental multiplication pattern: × 0.5, × 1, × 1.5, × 2, × 2.5. Applying this from the start: 24 × 0.5 = 12. So X = 12. To verify, the next step is X × 1: 12 × 1 = 12, which matches the term following X perfectly. The sequence works as: 24, 12, 12, 18, 36, 90.

Answer: (b).