Calculating Unique 5-Digit Numbers from Given List | Digits Probability Homework

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In summary, the conversation discusses the problem of finding unique 5-digit numbers from a given list of numbers, taking into account repeats and the restriction that zero cannot be the first digit. The suggested solution involves breaking it into cases based on the repeat counts of digits and considering the placement of the zero. The conversation also includes a proposed formula for counting the arrangements.
  • #1
member 428835

Homework Statement


how many 5 digit unique numbers can you make from the following list: [itex]1,2,2,3,3,4,5,6,6,6,0[/itex] and I assume zero cannot be first.

The Attempt at a Solution


since there are 11 numbers, typically i would say [itex]\frac{10!*10}{2!*2!*3!}[/itex] which would be the numbers over their repeats, but the problem is we have only 5 spots, not 11, and hence my problem.

thanks for your help!
 
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  • #2
I suggest breaking it into cases according to the repeat counts of digits. I.e. start with "full house", 3 of one (6s obviously) and 2 of another. For each pattern, count the number of ways of supplying the digits and multiply by the number of ways of sequencing them.
To deal with the zero, could permit it anywhere, then subtract off the number of 4-digit numbers not using the zero.
 
  • #3
so something like this (for now i'll ignore the zero): [tex]\underbrace{{2\choose1}\frac{5!}{2!3!}}_{\text{both full houses}}+\underbrace{{3\choose2}{3 \choose 1}\frac{5!}{2!2!}}_{\text{3 of the two pairs without a lone 6}}+\underbrace{{3\choose1}\frac{5!}{2!}}_{\text{three of the single pairs}}+\underbrace{{6\choose5}5!}_{\text{no pairs}}[/tex] is this correct (or at least close)? my choose notation is for selecting which of what to use and the factorials are for counting the arrangements once we have chosen what to use. again, I've disregarded zero for now, but I'm not sure this is complete even without zero. any help please!
 
  • #4
joshmccraney said:
so something like this (for now i'll ignore the zero): [tex]\underbrace{{2\choose1}\frac{5!}{2!3!}}_{\text{both full houses}}+\underbrace{{3\choose2}{3 \choose 1}\frac{5!}{2!2!}}_{\text{3 of the two pairs without a lone 6}}+\underbrace{{3\choose1}\frac{5!}{2!}}_{\text{three of the single pairs}}+\underbrace{{6\choose5}5!}_{\text{no pairs}}[/tex] is this correct (or at least close)? my choose notation is for selecting which of what to use and the factorials are for counting the arrangements once we have chosen what to use. again, I've disregarded zero for now, but I'm not sure this is complete even without zero. any help please!
The full house term (3+2) I agree with. For 2+2+1, you have a choice of 3 digit values for the pairs (3C2), but the single digit can then be any digit value not chosen: 5C1. Similarly in the 2+1+1+1 term.
 

1. How do I calculate the total number of unique 5-digit numbers from a given list?

To calculate the total number of unique 5-digit numbers from a given list, you need to use the formula nPr = n!/(n-r)!, where n is the number of digits in the list and r is the number of digits in the number. This will give you the total number of permutations, which is the total number of unique 5-digit numbers.

2. Can I use the same digit more than once when calculating unique 5-digit numbers?

Yes, you can use the same digit more than once when calculating unique 5-digit numbers. In fact, using the same digit multiple times will increase the number of possible combinations and ultimately result in a larger number of unique 5-digit numbers.

3. How do I determine the probability of getting a specific 5-digit number from a given list?

To determine the probability of getting a specific 5-digit number from a given list, you need to first calculate the total number of unique 5-digit numbers from the list using the nPr formula. Then, divide the number of times the specific number appears in the list by the total number of unique 5-digit numbers. This will give you the probability of getting that specific number.

4. Is there a limit to the number of unique 5-digit numbers that can be calculated from a given list?

Yes, there is a limit to the number of unique 5-digit numbers that can be calculated from a given list. The maximum number of unique 5-digit numbers that can be calculated from a list of n digits is n^5. This limit is reached when all possible combinations of the n digits are used to create the 5-digit numbers.

5. Can I use this method to calculate unique numbers with more or less than 5 digits?

Yes, you can use this method to calculate unique numbers with more or less than 5 digits. The nPr formula can be adjusted to accommodate different numbers of digits. For example, if you want to calculate unique 3-digit numbers from a given list, you would use the formula nPr = n!/(n-r)! where n is the number of digits in the list and r is the number of digits in the number (in this case, 3).

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