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Math Help - Whats the difference between these questions? Confused

  1. #1
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    Whats the difference between these questions? Confused

    Honestly these are 2 seperate questions but they look the same to me. Isnt non negative numbers, positive numbers? I dont even no how to go abouts solving this


    How many non negative integer solutions does the equation x+y+z+w=15 have?

    How many positive integer solutions does the equation x+y+z+w=15 have?
    ( hint: define new variables x'=x-1, y'=y-1, z'=z-1, w'=w'1)
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  2. #2
    A Plied Mathematician
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    Non-negatives = {0,1,2,3,...}
    Positives = {1,2,3,...}.
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  3. #3
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    The answer to the first is: the number of ways to put 15 identical items into four different cells.

    The answer to the second is: the number of ways to put 11 identical items into four different cells.
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