Math Problem Statement
A small combination lock on a suitcase has 5 wheels, each labeled with the 10 digits 0 to 9. How many 5 digit combinations are possible if no digit is repeated? If digits can be repeated? If successive digits must be different? Question content area bottom Part 1 a. The number of different 5 digit combinations possible if no digit is repeated is 30,240 . Part 2 b. The number of different 5 digit combinations possible if digits can be repeated is 100,000 . Part 3 c. The number of different 5 digit combinations possible if successive digits must be different is 7,290.
Solution
Let's walk through how to calculate each of these cases to verify the results:
Part 1: No digit is repeated
If no digit is repeated, we are selecting 5 digits out of 10. This is a permutation problem, where the order of the digits matters.
The formula for permutations when choosing elements from total elements is:
In this case:
- (the number of digits: 0-9)
- (we are selecting 5 digits)
The number of possible combinations is:
Calculating :
So, 30,240 is correct for this case.
Part 2: Digits can be repeated
If digits can be repeated, then each of the 5 wheels has 10 possible digits (0-9).
Since each position can be any of the 10 digits, the total number of combinations is:
So, 100,000 is also correct for this case.
Part 3: Successive digits must be different
If successive digits must be different, we are dealing with a slightly modified scenario. The first digit can be any of the 10 digits, but for each subsequent digit, it must be different from the previous one.
- For the first digit, there are 10 possible choices.
- For the second digit, there are 9 possible choices (it must be different from the first).
- For the third digit, there are again 9 choices (it must be different from the second but not necessarily from the first).
- For the fourth digit, there are 9 choices (different from the third).
- For the fifth digit, there are 9 choices (different from the fourth).
Thus, the total number of combinations is:
Calculating :
So, the total number of combinations is:
It seems like the value you provided (7,290) doesn't match this calculation. The correct number should be 65,610, not 7,290.
Would you like further details or clarification?
Follow-up questions:
- How would the calculations change if the lock had 6 wheels instead of 5?
- What if we were allowed to use only even digits for the combinations?
- How does the approach change if we must avoid two or more consecutive digits being the same?
- What is the probability of guessing the correct combination if digits can be repeated?
- How many combinations are possible if no two consecutive digits can differ by more than 1?
Tip:
When dealing with combinations and permutations, always verify if the order of the selection matters, as that dictates whether to use combinations or permutations.
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Math Problem Analysis
Mathematical Concepts
Permutations
Combinations
Counting Principle
Formulas
P(n, r) = n! / (n - r)! for permutations
Total combinations with repetition: 10^5
Total combinations with different successive digits: 10 * 9^4
Theorems
Fundamental Principle of Counting
Suitable Grade Level
Grades 9-12
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