If C(20, n + 2) = C(20, n – 2) then what is n equal to?

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NDA (Held On: 21 Apr 2019) Maths Previous Year paper
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  1. 8
  2. 10
  3. 12
  4. 16

Answer (Detailed Solution Below)

Option 2 : 10
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Concept:

The notation C(n, r) is the number of combinations/groups of n different things taking r at a time and is given by: C(n,r)=n!r!(nr)!

If C(n, x) = C(n, y), then x + y = n.

Calculation:

Given C(20, n + 2) = C(20, n – 2)

As we know that, if C(n, x) = C(n, y), then x + y = n.

⇒ (n + 2) + (n – 2) = 20

⇒ 2n = 20

⇒ n = 10
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