(a) Given digits are 3, 5, 7, 9. Since, the number of ways to find 5-digit numbers =5 ! but using 3,5,7,9 every time one-digit will be repeated. Hence number of 5-digit numbers with digit 3 repeated =
5!
2!
Number of 5-digit numbers with digit 5 repeated =
5!
2!
Number of 5-digit numbers with digit 7 repeated =
5!
2!
Number of 5-digit numbers with digit 9 repeated =