Multiple choice general knowledge math & puzzles

The difference between a number and its square is 870. What is the number?

  1. 42

  2. 29

  3. 30

  4. 32
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let the number be x. Then x^2 - x = 870, which gives x(x-1) = 870. Testing the options: 30^2 - 30 = 900 - 30 = 870, so 30 is the correct answer. The other options don't satisfy the equation: 29 gives 812, 32 gives 992, and 42 gives 1722.

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