Q. 4

# Mark the correct alternative in the following:

If , then *r* is equal to

A. 10

B. 11

C. 19

D. 12

Answer :

r + 1 + r – 1 = 20 ( ^{n}C_{x =} ^{n}C_{y} ⇒ n = x + y or x = y )

2r = 20

r = 10

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Prove that the product of 2n consecutive negative integers is divisible by (2n)!

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