What is n in this permutation, P(n, 3) = 60?

Please help me solve this.


closed as off-topic by heropup, SchrodingersCat, 3SAT, user228113, user99914 Jan 12 '16 at 17:20

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  • $\begingroup$ Could you add a little more detail? For example, what is the definition of $P(n,3)$? $\endgroup$ – Micapps Jan 7 '16 at 12:52
  • $\begingroup$ That's all there is in our 3rd grading exam i'm so sorry. $\endgroup$ – Stephen Mark Jan 7 '16 at 13:01

Its easy $\frac{n!}{(n-3)!}=60$ so $(n)(n-1)(n-2)=60$ we need to find three consecutive numbers whose product is $60$ so it can be easily seen that $5.4.3$ satisfy it thus $n=5$ .to cross check see $P(5,3)$

  • $\begingroup$ Thanks a lot for your help $\endgroup$ – Stephen Mark Jan 7 '16 at 13:04
  • $\begingroup$ Your welcome!!.. $\endgroup$ – Archis Welankar Jan 7 '16 at 13:09
  • $\begingroup$ But how about r is missing? What's the process? I really have a hard time with statistics hehehe $\endgroup$ – Stephen Mark Jan 7 '16 at 13:11
  • $\begingroup$ $r=3$ so it isnt missing $\endgroup$ – Archis Welankar Jan 7 '16 at 13:16

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