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Any 4 from 8 switch permutation

  1. Sep 13, 2011 #1
    Good evening to all
    I wonder if anyone can help please I have 8 switches b1,b2,b3,b4,b5,b6,b7,b8 I am trying to work out how many permutations I would have if I pressed any 4 of the 8 switches ie if I pressed b1,b3,b,7,b8 to make a circuit or it could be b3,b5,b6,b7 doing it by long hand I reckon it is 40 combination.
    I fully understand if no one wishes to answer the question but I am completely useless at maths
    Thank you to all
     
  2. jcsd
  3. Sep 13, 2011 #2
    8!/(4!4!)=70
     
  4. Sep 14, 2011 #3
    Thankyou Robert will have to get paper and pencil out again
     
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