Solution: A four-digit number ranges from 1000 to 9999. A number is divisible by 5 if its last digit is 0 or 5. The smallest four-digit number divisible by 5 is 1000, and the largest is 9995. These form an arithmetic sequence with first term 1000, common difference 5, and last term 9995. The number of terms is given by \(\frac{9995 - 1000}{5} + 1 = \frac{8995}{5} + 1 = 1799 + 1 = 1800\). Therefore, there are \(\boxed{1800}\) four-digit numbers divisible by 5.

["Understanding Four-Digit Numbers Divisible by 5: The Mathematical Solution", "Four-digit numbers range from 1000 to 9999 — an extensive range with a fascinating mathematical property: every fifth number is divisible by 5. But how many exactly? Let’s explore the full breakdown of these special numbers and uncover the elegant math behind their total count.", "### What Does It Mean for a Number to Be Divisible by 5?", "A whole number is divisible by 5 if and only if its last digit is either 0 or 5. This simple rule allows us to identify all four-digit multiples of 5 with precision.", "### Defining the Sequence", "All four-digit numbers divisible by 5 form a well-defined arithmetic sequence:", "- First term ( a = 1000 )\n- Common difference ( d = 5 )\n- Last term ( l = 9995 )", "This sequence starts at 1000 (the smallest four-digit number divisible by 5) and ends at 9995 (the largest).", "### Applying the Arithmetic Sequence Formula", "To find how many such numbers exist, we use the formula for the number of terms in an arithmetic sequence:", "[\nn = \frac{l - a}{d} + 1\n]", "Substituting the known values:", "[\nn = \frac{9995 - 1000}{5} + 1 = \frac{8995}{5} + 1 = 1799 + 1 = 1800\n]", "So, there are exactly 1800 four-digit numbers divisible by 5.", "### Why This Count Matters", "This kind of counting isn't just a theoretical exercise — it’s essential in fields like computer science, cryptography, and algorithm design, where modular arithmetic and periodic patterns play key roles. Recognizing countable subsets of numbers simplifies problem-solving and enables efficient data processing.", "### Summary", "- Four-digit numbers range from 1000 to 9999\n- Every 5th number is divisible by 5\n- They form an arithmetic sequence starting at 1000, ending at 9995, with a common difference of 5\n- The total number of such numbers is (\boxed{1800})", "Understanding this sequence unlocks a deeper appreciation for number patterns and paves the way for solving more complex mathematical challenges."]