Math Problem Statement

How many such numbers are possible if the number is greater than 40,000 (digits cannot be repeated)?

Solution

To solve this question, let’s break it into steps based on the given problem and solution:

Question Recap:

We are tasked to find how many five-digit numbers are possible if the number is greater than 40,000 and digits cannot be repeated.


Step-by-Step Solution:

  1. Analyze the first digit:

    • To ensure the number is greater than 40,000, the first digit (most significant) must be 4, 5, 6, 7, 8, or 9. That gives 6 options.
  2. Second digit selection:

    • Once the first digit is chosen, we have 9 remaining digits to pick from (since repetition is not allowed). This gives 9 options for the second digit.
  3. Third digit selection:

    • After selecting the first and second digits, 8 digits remain to choose from, so there are 8 options for the third digit.
  4. Fourth digit selection:

    • Now, 7 digits remain, providing 7 options for the fourth digit.
  5. Fifth digit selection:

    • Finally, 6 digits remain, so there are 6 options for the fifth digit.

Total Calculation:

The total number of five-digit numbers is:

6×9×8×7×6=2,1606 \times 9 \times 8 \times 7 \times 6 = 2,160

This matches the solution provided in the image.


Final Answer:

There are 2,160 five-digit numbers greater than 40,000 where digits cannot be repeated.


Let me know if you'd like further clarification or additional examples.
Here are 5 related questions for practice:

  1. How many five-digit numbers less than 50,000 can be formed without repeating digits?
  2. What is the total number of five-digit numbers possible without repeating digits?
  3. How many six-digit numbers greater than 100,000 can be formed without repeating digits?
  4. What happens to the count if the restriction of non-repeating digits is removed?
  5. How many numbers greater than 40,000 can be formed if only odd digits are allowed?

Tip: Always identify and limit the options for the most restrictive digit(s) first when solving digit-based problems.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Permutations
Number theory
Counting principles

Formulas

Total combinations = product of choices for each digit

Theorems

Basic principles of permutations and combinations

Suitable Grade Level

Grades 8-10