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How many different ways…?

4 មតិ Posted by ​នៅ ខែកញ្ញា 26, 2012

How many different ways can 2 students be seated in a row of 4 desks, so that there is always at least one empty desk between the students?

  • A   2
  • B   3
  • C   4
  • D   6
  • E    12
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4 responses to “How many different ways…?”

  2. គឹម ចាន់ ខែតុលា 2, 2012 ម៉ោង 10:31 ព្រឹក

    Ans d) – 6 ways

    Assume A & B are 2 students and x as empty space, then we have the following possible combinations:

    A x B x
    A x x B
    x A x B
    B x A x
    B x x A
    x B x A

    One more way:
    Since this is a combination it can be also solved also by applying the combination formula

    nCr = n!/ (n-r)!*r!

    we have n = 4 and r = 2

    nCr= 4*3*2*1/ ( 4-2) ! * 2 *1
    = 4*3/ 2*1 = 6

    ឆ្លើយតប

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