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If nC r - 1 = 36, nC r = 84 and nC r + 1 = 126 then?

Correct Answer: n = 9, r = 3

Explanation:

nCr - 1 = 36, nCr = 84 and nCr + 1 = 126
nCr / nCr - 1 = 84/36
⇒ 3n - 10r + 3 = 0 ....(i)
nCr + 1 / nCr = 126/84
⇒ 2n - 5r - 3 = 0 .............(ii)
From (i) and (ii) r = 3, n = 9


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