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Discrete Mathematics

Rule of Sum and Rule of Product

Rule of Sum and Rule of Product: Level 2 Challenges



When we write the integers from 1 to 100, how many times does the digit 9 appear?


Find the number of \(2\) digit numbers whose digit sum is a perfect square.

If you take a \(3 \times 3 \times 3\) Rubik cube and break it up into the \( 3^3 \) cubes, how many cubes would have stickers on exactly \(2\) faces?

Bonus question: Can you generalize this for a \(N \times N \times N\) Rubik cube?


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