Math Problem Statement

How many 4-digit numbers can be formed using the digits 1, 5, 3, 7, 8 without repetition, which are divisible by 5?

Solution

Let's solve the problem step by step.

Problem:

We need to determine how many 4-digit numbers can be formed using the digits 1,5,3,7,81, 5, 3, 7, 8 without repetition such that the numbers are divisible by 5.


Key Concepts:

  1. Divisibility by 5: A number is divisible by 5 if its last digit is either 00 or 55. In this case, since 00 is not in the set of digits, the last digit must be 5.

  2. Formation of 4-digit numbers:

    • Since the last digit is fixed as 55, we are left with the digits 1,3,7,81, 3, 7, 8 to arrange in the first three places.
    • These remaining digits can be arranged in different orders to form valid numbers.
  3. Permutation Calculation:

    • The number of ways to arrange nn distinct objects is given by n!n! (factorial of nn).
    • Here, we have 44 digits (excluding 55) to arrange in 44 positions, so the number of arrangements is 4!4!.

Solution:

  1. Fix 55 as the last digit.
  2. Arrange the remaining 44 digits (1,3,7,81, 3, 7, 8) in the first 33 positions: Number of ways=4!=24\text{Number of ways} = 4! = 24

Thus, there are 24 such numbers.


Final Answer:

The correct option is: (1) 24


Would you like a detailed explanation of permutations or help with similar problems? Here are some related questions to expand on:

  1. How many 4-digit numbers can be formed using the same digits if repetition is allowed?
  2. How many 4-digit numbers divisible by 22 can be formed from the digits 1,5,3,7,81, 5, 3, 7, 8?
  3. How many 5-digit numbers can be formed without repetition using these digits?
  4. How does the condition of divisibility by 55 change if 00 is included in the digits?
  5. How many numbers are divisible by 33 when formed using these digits?

Tip: Always identify constraints (like divisibility rules or digit repetition) before solving permutation problems.

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Math Problem Analysis

Mathematical Concepts

Divisibility rules
Permutations
Factorials

Formulas

n! = n × (n-1) × (n-2) × ... × 1
Divisibility rule for 5: A number is divisible by 5 if its last digit is 0 or 5

Theorems

Fundamental Counting Principle
Permutation Theorem

Suitable Grade Level

Grades 8-10