11For the second sum, u may see http://www.artofproblemsolving.com/Forum/viewtopic.php?f=513&t=348532.
Phenomenal soln!
1)There are seven people in a elevator.The lift stops at 3(unspecified) floors.In each stop or more people get out, but no one boards it.After 3 stops it is found that the elevator is empty.Find the no. of way this can happen..................
Ans...1806
2)There are 100 people waiting to enter a hall in which the seats are numbered 1 to 100.The 1st person enters and takes any seat of his choice.There on each person enters the hall and sits in corresponding numbered seat(eg.2nd person enters and takes seat-2) IF AVAILABLE, AND IF NOT THEN TAKES ANY OTHER SEAT.Find the no. of ways the arrangement of the persons in the room is possible.................
Source:ISI(BStat 2010)
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UP 0 DOWN 0 0 5
5 Answers
11
62no arka.. that is not the right way bcos it will mean you are not differentiating betwen the 7 people
Each person has 3 options to get down..
So 37 ways..= 2187
We have to remove those cases when no one gets out at a particular floor.. (Inclusion Exclusion or Venn Diagram approach)