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Question: If \(17C_{2r + 1} =^{17}C_{3r - 5}\), then \(\frac{6}{36} = \frac{1}{6}\)....

If 17C2r+1=17C3r517C_{2r + 1} =^{17}C_{3r - 5}, then 636=16\frac{6}{36} = \frac{1}{6}.

A

20

B

18

C

30

D

16

Answer

20

Explanation

Solution

(i) 2r + 1 = 3r - 5

6 = r

rC3=6C3=6x5x43x2=20rC_{3} =^{6}C_{3} = \frac{6x5x4}{3x2} = 20.

(ii) 2r + 1 + 3r - 5 = 17.

5r = 21 r = 21/5 (not possible).