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Problem #64 · September 29, 2026

Natural numbers

Find the sum of the digits of the following number. 1234567891011…29301234567891011 \ldots 2930
  1. A160160
  2. B168168
  3. C150150
  4. D170170

WORKED EXAMPLE

Solution

The number is formed by writing the numbers from 11 to 3030 in succession. 1..91..9 — 4545; 10..1910..19 — tens 1010 and ones 4545, in total 5555; 20..2920..29 — tens 2020 and ones 4545, in total 6565; 3030 — 33. Altogether: 45+55+65+3=16845+55+65+3=168.
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