# If 28C2r : 24C2r – 4 : 225 : 11, find r.

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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