400 is the predecessor of ____.
401
Step 1: What does predecessor mean?
Predecessor means the number that comes just before a given number (one less than it).
Rule: \(\text{Predecessor of } n = n - 1\)
Step 2: Set up the situation
400 is the predecessor of some number. Let that number be \(x\).
So, \(x - 1 = 400\).
Step 3: Solve for \(x\)
Add 1 to both sides:
\(x = 400 + 1\)
\(x = 401\)
Step 4: Quick check
Is the predecessor of 401 equal to 400?
\(401 - 1 = 400\) ✔️
Therefore, the missing number is 401.