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1st Day at school

  1. Jan 10, 2007 #1
    It was Cheryl's first day at school. The teacher suggested that it would be a good idea for each child to meet every other child in the class. The teacher said, "When you meet, please shake hands and introduce yourself by name."

    If there were 15 children in the class, how many total handshakes were there?
    :uhh:
     
  2. jcsd
  3. Jan 10, 2007 #2
    [tex]\sum_{i=1}^{15}i[/tex]
     
  4. Jan 10, 2007 #3
    No.....Slightly wrong
     
  5. Jan 10, 2007 #4

    Hootenanny

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    14.............
     
  6. Jan 10, 2007 #5
    14...................?
     
  7. Jan 10, 2007 #6
  8. Jan 10, 2007 #7

    Hootenanny

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    I thought it was only Cheryl's first day, therefore all the other children would already know each other.

    If not the answer must be 210.
     
  9. Jan 10, 2007 #8
    no.......sorry
     
  10. Jan 10, 2007 #9
    Lol I thought way too fast... 105!
     
  11. Jan 10, 2007 #10
    Ya..Now it's Correct........
     
  12. Jan 10, 2007 #11

    Hootenanny

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    hmm, could someone explain this one to me?

    Hey dontdistrbmycircles :)
     
  13. Jan 10, 2007 #12
    may I do that?
     
  14. Jan 10, 2007 #13
    Sure, the first boy shakes 14 hands right? Then the next shakes 13 until you get to 1, my original sum should have read [tex]\sum_{i=1}^{14}i[/tex] :P

    Keeps going down one because the same person does not shake the same person's hand twice.
     
  15. Jan 10, 2007 #14
    Ya right....
    The class has 15 children. The first

    child shakes hands with the other 14

    children. The second child has already

    shaken hands with the first child, and so

    has to shake hands with only the other 13

    children. In this manner, the

    second-last child has to shake hands with

    only one child, and the last child has

    already met all the children. Thus, the

    number of handshakes is

    14 + 13 + ........ + 2 + 1 = 105.

    If there were 15 children in the class,

    then there were 105 total handshakes.
     
  16. Jan 10, 2007 #15

    Hootenanny

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    Damn it :grumpy:. Thanks!
     
  17. Jan 10, 2007 #16
    Oh....Am I correct?
     
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