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Find the value of "^nC(r-1)//"^nCr...

Find the value of `"^nC_(r-1)//"^nC_r`

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`"^nC_(r-1)//^nC_r = n!//(r-1)!(n-r+1)!//n!//r!(n-r)!`
`r!(n-r)!//(r-1)!(n-r+1)!`
= `r!(r-1)!(n-r)!//(r-1)!(n-r+1)(n-r)!`
`r/n-r+1`
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