Math Problem Statement

Find the number of five-digit numbers with distinct digits which do not contain 4, 6, or 7.

Solution

To solve the problem:

We are tasked with finding the number of five-digit numbers with distinct digits that do not include the digits 4, 6, or 7.

Step-by-Step Solution:

  1. Available digits: The total digits are {0,1,2,3,5,8,9}\{0, 1, 2, 3, 5, 8, 9\}. These exclude {4,6,7}\{4, 6, 7\}, leaving us with 7 digits.

  2. Creating five-digit numbers:

    • A five-digit number cannot start with 00 (as it would no longer be a five-digit number).
    • So, for the first digit, we have 66 valid choices ({1,2,3,5,8,9}\{1, 2, 3, 5, 8, 9\}).
    • For the second digit, we have 66 remaining choices (since one digit is already used, and 00 is now valid).
    • For the third digit, 55 choices remain.
    • For the fourth digit, 44 choices remain.
    • For the fifth digit, 33 choices remain.
  3. Calculation:

    • The total number of valid five-digit numbers is: 6×6×5×4×3=21606 \times 6 \times 5 \times 4 \times 3 = 2160

Final Answer:

There are 2160 five-digit numbers with distinct digits that do not contain 44, 66, or 77.


Do you need further explanation or breakdowns?

Related Questions:

  1. How would the calculation change if all digits were allowed?
  2. How many such numbers would there be if repetition of digits were allowed?
  3. What if the number must begin with an odd digit?
  4. How many four-digit numbers can be formed under similar restrictions?
  5. Can you derive a general formula for nn-digit numbers under these constraints?

Tip:

When solving combinatorics problems, always identify constraints like digit exclusions and ordering restrictions to narrow the scope effectively.

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Math Problem Analysis

Mathematical Concepts

Combinatorics
Permutations
Digit Restrictions

Formulas

Total permutations: n! / (n-r)! for selecting r objects from n total objects

Theorems

Basic principles of counting

Suitable Grade Level

Grades 9-12