Digit Permutations 17D640
1. **Problem statement:** We have digits 2, 4, 5, 7, and 9 and want to find:
- Total numerals formed using all digits without repetition.
- How many are multiples of 5.
- How many are even.
- How many are greater than 70,000.
- How many are less than 50,000.
2. **Total numerals formed:** Using all 5 digits without repetition means arranging 5 distinct digits in all possible orders.
Formula: Number of permutations of $n$ distinct digits = $n!$
Here, $n=5$, so total numerals = $5! = 120$
3. **Multiples of 5:** A number is divisible by 5 if its last digit is 0 or 5. Since 0 is not in our digits, last digit must be 5.
Fix last digit as 5, arrange remaining 4 digits in any order.
Number of such numbers = $4! = 24$
4. **Even numbers:** Even numbers end with an even digit. Our even digits are 2 and 4.
Case 1: Last digit is 2, arrange remaining 4 digits in any order: $4! = 24$
Case 2: Last digit is 4, arrange remaining 4 digits: $4! = 24$
Total even numbers = $24 + 24 = 48$
5. **Numbers greater than 70,000:** The first digit must be 7 or 9 (since 2,4,5 are less than 7).
Case 1: First digit 7, arrange remaining 4 digits: $4! = 24$
Case 2: First digit 9, arrange remaining 4 digits: $4! = 24$
Total numbers > 70,000 = $24 + 24 = 48$
6. **Numbers less than 50,000:** The first digit must be 2 or 4 (digits less than 5).
Case 1: First digit 2, arrange remaining 4 digits: $4! = 24$
Case 2: First digit 4, arrange remaining 4 digits: $4! = 24$
Total numbers < 50,000 = $24 + 24 = 48$
**Final answers:**
- Total numerals: 120
- Multiples of 5: 24
- Even numbers: 48
- Numbers > 70,000: 48
- Numbers < 50,000: 48