यदि 2nC3 : nC2 = 12 : 1 है, तो n का मान ज्ञात कीजिए।

  1. 2
  2. 3
  3. 5
  4. 7

Answer (Detailed Solution Below)

Option 3 : 5
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संकल्पना:

एक समय (r ≤ n) में r लिए गए n विशिष्ट वस्तुओं के सभी संयोजनों की संख्या निम्न है:

\(^{n}C_{r}=\frac{n!}{(n-r)!r!}\)

गणना:

चूँकि 2nC3 : nC2 = 12 : 1

\(⇒ \frac{2n!}{(2n-3)!\space 3!}:\frac{n!}{(n-2)!\space 2!}=12:1\)

\(⇒ \frac{2n(2n-1)(2n-2)}{3\times 2\times 1}:\frac{n(n-1)}{2\times 1}=12:1\)

⇒ 2n - 1 = 9

⇒ n = 5

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