The smallest 4-digit number is the successor of the largest 3-digit number.
Step 1: The largest 3-digit number is (999).
Step 2: “Successor” means “the next number,” i.e., add (1).
( ext{Successor of }999 = 999 + 1)
Step 3: Calculate:
(999 + 1 = 1000)
Step 4: The smallest 4-digit number is (1000).
Conclusion: Since (999) becomes (1000) after adding (1), the statement is true.