InterviewSolution
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If `^n P_r=^n P_(r+1)a n d^n C_r=^n C_(r-1,)`then thevalue of `n+r`is. |
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Answer» `.^(n)C_(r) = .^(n)C_(r-1)` `rArr n = r +(r-1)` `rArr n = 2r - 1` ...(1) and `.^(n)P_(r)- .^(n)P_(r+1)` `rArr (n!)/((n-r)!) =(n!)/((n-r-1)!)` `rArr (n-r)! = (n-r-1)!` `rArr (n-r)(n-r-1)! = (n-r-1)!` `rArr n- r = 1` `rARr 2r - 1 - r = 1` [From eq. (1)] `rArr r = 2` `rArr` From eq. (1) `n = 2r - 1` `=2(2) - 1 = 3` `n = 3, r = 2` |
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