What is X in the sequence 24, X, 12, 18, 36, 90?

What is X in the sequence 24, X, 12, 18, 36, 90?
  1. 18
  2. 12
  3. 9
  4. 6

Solution

The terms are obtained by multiplying with increasing factors: $12\times1.5=18$, $18\times2=36$, $36\times2.5=90$. The multipliers form the pattern $0.5, 1, 1.5, 2, 2.5$. Then $24\times0.5 = 12 = X$ and $X\times1 = 12$, consistent. Hence X = 12.

Asked in: CSAT 2025

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