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anonymous

  • one year ago

A professor must randomly select 4 students to participate in a mock debate. There are 15 students in his class. In how many different ways can these students be selected, if the order of selection does not matter?

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  1. jim_thompson5910
    • one year ago
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    Let's say you had 4 slots: A,B,C,D how many choices do you have for slot A?

  2. anonymous
    • one year ago
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    15

  3. jim_thompson5910
    • one year ago
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    how many do you have for slot B?

  4. anonymous
    • one year ago
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    15

  5. jim_thompson5910
    • one year ago
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    once you pick a person, you cannot pick them again so you have 15-1 = 14 choices for slot B

  6. jim_thompson5910
    • one year ago
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    how about slot C?

  7. anonymous
    • one year ago
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    13

  8. jim_thompson5910
    • one year ago
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    and slot D?

  9. anonymous
    • one year ago
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    omg i get it now thank you

  10. jim_thompson5910
    • one year ago
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    what result do you get

  11. anonymous
    • one year ago
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    32760

  12. jim_thompson5910
    • one year ago
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    that would be the answer if order mattered but order does NOT matter

  13. jim_thompson5910
    • one year ago
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    if you had 4 students, call them A,B,C,D then ABCD is the same as ACBD and ADCB there are 4! = 4*3*2*1 = 24 ways to rearrange ABCD. So we have to divide by 24 to make the correction

  14. jim_thompson5910
    • one year ago
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    32760/24 = 1,365

  15. jim_thompson5910
    • one year ago
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    there are 1,365 different ways to pick 4 people (order doesn't matter)

  16. anonymous
    • one year ago
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    oh okay thank you

  17. jim_thompson5910
    • one year ago
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    you're welcome

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