A four-digit number is called delightful if it is divisible by 25, the sum of its digits is divisible by 25, and the product of its digits is divisible by 25. Find all delightful numbers.
5875 and 8575
The sum of the digits of a four-digit number does not exceed 36, so for a delightful number, it must be 25. Since a delightful number is divisible by 25, it ends in either 00, 50, 25, or 75. If a four-digit number ends in 00 or 50, the sum of its digits does not exceed 9 + 9 + 5 = 23, which is not suitable. If a delightful number ends in 25, the sum of the first two digits must be 18. This could only be the number 9925, but its product of digits is not divisible by 25. Therefore, a delightful number can only end in 75. In this case, the sum of its first two digits is 13, and their product must be divisible by 5. Thus, these two digits are 5 and 8 (in any order).