UPSC Prelims 2025 CSAT Paper II · Q78 of 78 Mental Ability medium

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

  1. (a) 0
  2. (b) 3
  3. (c) 6
  4. (d) 9 ✓ UPSC's answer

Why the answer is (d)

• The first 9 digits are 1 to 9.

• The next 180 digits are 10 to 99, giving 189 digits total.

• The 489th digit is therefore the 300th digit in the 3-digit numbers starting from 100.

• Since 300 ÷ 3 = 100, it is the last digit of the 100th 3-digit number.

• The 100th 3-digit number is 199, so the 489th digit is 9, option (d).

Why the other options are wrong

(a) 0
The 489th digit is the third digit of 199, which is 9, not 0.
(b) 3
The 489th digit is the third digit of 199, which is 9, not 3.
(c) 6
The 489th digit is the third digit of 199, which is 9, not 6.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2025, held on 25 May 2025. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.

Reading the answer is not the same as getting it right under a clock. Practise this question with UPSC's negative marking, and anything you miss goes into an error notebook until you get it right twice.

Practise this paper free