Final answer:
The number the student is referring to is 555555. This number is a palindrome (it reads the same forwards and backwards), its digits add up to 30, and when rounded to the nearest hundred thousand, it becomes 600,000.
Step-by-step explanation:
The number the student is referring to is a unique number that meets all three conditions: its digits add up to 30, it can be read the same way forwards or backwards (making it a palindrome), and when rounded to the nearest hundred thousand, it becomes 600,000. The only number that fits all these criteria is 555555. Here's how: 
 
- The digits in 555555 sum to 30 (5+5+5+5+5+5=30).
  - It can be read the same way both forwards and backwards, making it a palindromic number.
  - When rounded to the nearest hundred thousand, it becomes 600,000.
 
Learn more about Number Properties