UPSC Prelims 2019·CSAT·Logical Reasoning·Series and Sequences

What is X in the sequence 4, 196, 16, 144, 36, 100, 64, X?

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Last updated 23 May 2026, 3:31 pm IST
  1. A48
  2. B64Correct
  3. C125
  4. D256

Explanation

The given sequence is an alternating series consisting of two separate patterns. The first pattern involves the numbers at odd positions: 4, 16, 36, and 64. These are the squares of consecutive even numbers: 2 squared is 4, 4 squared is 16, 6 squared is 36, and 8 squared is 64. The second pattern involves the numbers at even positions: 196, 144, 100, and X. These are the squares of even numbers in descending order: 14 squared is 196, 12 squared is 144, and 10 squared is 100. Following this descending even number pattern, the next number for X should be the square of 8. Since 8 squared is 64, the value of X is 64.
Logical Reasoning: What is X in the sequence 4, 196, 16, 144, 36, 100, 64, X?
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