Multiple choice general knowledge math & puzzles

What 5-digit number has the following features: If we put the numeral 1 at the beginning, we get a number three times smaller than if we put the numeral 1 at the end of the number.

  1. 14285

  2. 42700

  3. 42857

  4. 10000
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let the 5-digit number be N. If we put 1 at the end, we get 10N + 1. If we put 1 at the beginning, we get 100000 + N. The condition says 100000 + N = 3(10N + 1), which simplifies to 100000 + N = 30N + 3, giving 99997 = 29N, so N = 42857.

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