One number doesn't match this factorial series: 2, 6, 24, 120, 720, 1000

Question

One number doesn't match this factorial series: 2, 6, 24, 120, 720, 1000

1. A. 6
2. B. 24
3. C. 1000 (Correct answer)
4. D. 120

Correct Answer

Option C — 1000

Detailed Solution & Explanation

The correct answer is 1000.

Key Points

• The series lists factorials:
  • 2! = 2, 3! = 6, 4! = 24, 5! = 120, 6! = 720
• The next factorial would be 7! = 5040, not 1000.
• 1000 is therefore the term that does not belong.

Additional Information

• A factorial is the product of all positive integers up to n: 5! = 5 × 4 × 3 × 2 × 1 = 120. By convention 0! = 1.
• Factorials worth memorising: 1, 2, 6, 24, 120, 720, 5040, 40320 — they grow far faster than powers, which is what makes an out-of-place round number conspicuous.
• A round figure such as 1000 sitting among factorials is a strong visual clue; factorials from 5! onward always end in 0 but are never simple powers of ten.

प्रश्न (हिन्दी में)

एक संख्या इस क्रमगुणित श्रृंखला से मेल नहीं खाती: 2, 6, 24, 120, 720, 1000

1. A. 6
2. B. 24
3. C. 1000
4. D. 120