555

Not sure what you want with “555.” Here are a few quick possibilities in case one matches your goal:

• Arithmetic: 5 + 5 + 5 = 15; 5 × 5 × 5 = 125; 555 = 3 × 5 × 37.
• Divisibility: 555 is divisible by 3 and by 5 (sum of digits 15; ends with 5).
• Roman numerals: 555 = DLV.
• Binary: 555 in binary is 1000101011.
• It’s a repdigit (three identical digits).

If you meant a specific exam topic or a particular problem, tell me the subject and what you’d like (e.g., factorization, base conversion, quick proofs), and I’ll tailor a quick practice item.