Q. 115.0( 4 Votes )

# If ^{28}C_{2r} : ^{24}C_{2r – 4} : 225 : 11, find r.

Answer :

Given:

⇒

We know that

And also n! = n(n – 1)(n – 2)…………2.1

⇒

⇒

⇒

⇒

⇒ (2r)(2r – 1)(2r – 2)(2r – 3) = 11 × 12 × 13 × 14

Equating the corresponding terms on both sides we get,

⇒ 2r = 14

⇒

⇒ r = 7

∴ The value of r is 7.

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