What will come in place of the question mark? 1, 9, 25, 49, ?, 121

Question

What will come in place of the question mark? 1, 9, 25, 49, ?, 121

1. A. 100
2. B. 91
3. C. 64
4. D. 81 (Correct answer)

Correct Answer

Option D — 81

Detailed Solution & Explanation

The correct answer is 81.

Key Points

• This series is built from the squares of consecutive odd numbers.
• Series: 1, 9, 25, 49, ?, 121
• 1 = 1²
• 9 = 3²
• 25 = 5²
• 49 = 7²
• ? = 9² = 81
• 121 = 11²
• The bases are the odd numbers 1, 3, 5, 7, 9, 11, so the missing term is 9² = 81.
• recognising perfect squares (and their odd/even patterns) is essential for number-series questions.
• The squares of odd numbers (1, 9, 25, 49, 81, 121) are all odd and grow with a gap that itself increases by 8 each time.

Exam Tip

• memorise squares up to at least 20² = 400 and cubes up to 12³ = 1728 — most JKSSB, SSC and railway series questions are disguised square or cube patterns.