Q. What is the 489th digit in the number 123456789101112…?

Explanation : 

1. Count digits in the 1-digit numbers (1 to 9):
• 9 numbers × 1 digit = 9 digits

2. Count digits in the 2-digit numbers (10 to 99):
• 90 numbers × 2 digits = 180 digits
• Cumulative total so far = 9 + 180 = 189 digits

3. Since 489 > 189, the 489th digit lies in the 3-digit numbers (100, 101, 102, …).
• Digits to go into the 3-digit block: 489 – 189 = 300

4. Each 3-digit number contributes 3 digits.
• 300 ÷ 3 = 100 exactly, so the 300th digit in this block is the 3rd digit of the 100th 3-digit number.
• The first 3-digit number is 100, so the 100th one is 100 + 100 – 1 = 199.

5. The 3rd (last) digit of 199 is 9.

Therefore, the 489th digit is 9.