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Question
If `""^15"C"_(2"r" - 1) = ""^15"C"_(2"r" + 4)`, find r
Solution
Given `""^15"C"_(2"r" - 1) = ""^15"C"_(2"r" + 4)`
We have nCx = nCy
⇒ x = y or x + y = n
`""^15"C"_(2"r" - 1) = ""^15"C"_(2"r" + 4)`
⇒ (2r – 1) + (2r + 4) = 15
4r + 3 = 15
⇒ 4r = 12
r = `12/4`
= 3
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