23 Aug, 05:45PM in sunny Singapore!

PnC

Subscribe to PnC 10 posts

Please Login or Signup to reply.
  • ohnoez!'s Avatar
    528 posts since May '07
    • there is a committee of 5 boys and 3 girls. at a meeting, 2 boys are absent. find the no. of ways they can sit at a round table with 8 seats.

      ans is 2520

      a deck of 10 cards is numbered from 0 to 9. find the no. of ways 5 cards can be chosen such that the sum of the chosen cards is larger than those not chosen.

      ans is 126

      how to dooooooooooo? pls give explanations! thx!

  • laurence82's Avatar
    124,680 posts since Nov '03
  • ohnoez!'s Avatar
    528 posts since May '07
  • Mountain Dew's Avatar
    167 posts since Aug '10
    • This is the additional maths topics right? It brings back my memories back to sec school.

  • ohnoez!'s Avatar
    528 posts since May '07
  • Mountain Dew's Avatar
    167 posts since Aug '10
    • Originally posted by ohnoez!:

      its h2 maths lol....


      Lastime additional maths teachers got teach this topic. Now u all learn in JC?

      Edited by Mountain Dew 27 Aug `10, 11:02AM
  • quailmaster's Avatar
    110 posts since Jul '07
    • for the 1st question

      the no of ways to arrange 6 people in 8 seats is 8P6

      as they are seated in a circle we need to divide by 8

      hence the ans 8P6 / 8 = 2520

    • for the 2nd question

      there are 10C5 ways of choosing 5 cards without restriction

      the 5 cards chosen is either bigger than or lesser than the cards not chosen

      the probability that the chosen cards are greater than the "un chosen" cards is equal to  the probability that the chosen cards are lesser than the "unchosen" cards

      hence we can just take 10C5 divide by 2 = 126

  • Moderator
    eagle's Avatar
    23,320 posts since Aug '01
    • Originally posted by quailmaster:

      for the 1st question

      the no of ways to arrange 6 people in 8 seats is 8P6

      as they are seated in a circle we need to divide by 8

      hence the ans 8P6 / 8 = 2520

      Nice.

      We can also factorial 8 different seats, but 2 are "repeated" as empty seats

      Hence, the answer is

      (8 - 1)! / 2! =2520

  • SBS n SMRT's Avatar
    4,506 posts since Mar '08
    • eh, these two are the lecutre examples used by my teacher  in my lecture notes......

Please Login or Signup to reply.