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Floor and Ceiling (Hard)

Late AMC 10/12 through early AIME — dense computation.

Floor and Ceiling: core idea

Sums of floors.

Example problem: hint and answer

Find ⌊200⌋\lfloor\sqrt{200}\rfloor.

Hint: Convert a floor or ceiling statement into its defining interval. Answer: 14.

Practice (9 problems — type your answers)

  • 1. How many integers nn satisfy ⌊n/3⌋=7\lfloor n/3\rfloor=7?

  • 2. Find ⌈100/7⌉\lceil100/7\rceil.

  • 3. Find ∑k=110⌊k/3⌋\sum_{k=1}^{10}\lfloor k/3\rfloor.

  • 4. How many integers nn satisfy 0<⌊(n+2)/5⌋<40<\lfloor(n+2)/5\rfloor<4?

  • 5. Find ⌊1/(2−1)⌋\lfloor1/(\sqrt2-1)\rfloor.

  • 6. Find greatest nn with ⌈n/4⌉=9\lceil n/4\rceil=9.

  • 7. How many nonnegative lattice points satisfy x+y≤7x+y\le7?

  • 8. Find ⌊999/13⌋+⌈999/13⌉\lfloor999/13\rfloor+\lceil999/13\rceil.

  • 9. Find ⌊50+8⌋\lfloor\sqrt{50}+\sqrt8\rfloor.

Floor and Ceiling Practice Problems — Hard