मराठी
Karnataka Board PUCPUC Science Class 11

Permutations

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Estimated time: 4 minutes
Maharashtra State Board: Class 12

Key points: Permutations

When all the objects are distinct

  • \[^nP_r\mathrm{~or~}P(n,r).\mathrm{~i.e.~}P\left(n,r\right)={}^nP_r=\frac{n!}{\left(n-r\right)!},0\leq r\leq n\]
  • Repetition Allowed: nn
  • Objects Together: 2(n − 1)!
  • Specified Object Included: \[r\times^{(n-1)}P_{(r-1)}\]

When some objects are identical

  • Identical objects (p same, rest distinct): \[\frac{n!}{p!}\]
  • Multiple identical objects: \[\frac{n!}{p_{1}!p_{2}!\ldots p_{k}!}\]

Special Cases:

  • \[^nP_n\] = \[\mathrm{n!}\]
  • \[{}^{\mathrm{n}}\mathrm{P}_{0}=1\]
  • \[^nP_1\] = n
  • \[{}^{n}P_{n-1}\]= n!
  • \[^nP_r\] = \[\mathrm{^{n-1}P_r+r.^{n-1}P_{r-1}}\]

Shaalaa.com | Theorem of permutation and combination

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