2003 AIME I Problem 1

Attempt Problem 1 of the 2003 AIME I below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2003 AIME I solutions, or check the answer key.

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1.

Given that ((3!)!)!3!=kn!,\frac{((3!)!)!}{3!} = k \cdot n!, where kk and nn are positive integers and nn is as large as possible, find k+n.k + n.

Answer: 839
Concepts:factorialbounding to limit cases
Difficulty rating: 1670
Solution:

Since 3!=63! = 6 and 6!=720,6! = 720, the expression is ((3!)!)!3!=720!6=720719!6=120719!. \begin{aligned} \frac{((3!)!)!}{3!} &= \frac{720!}{6} \\ &= \frac{720 \cdot 719!}{6} \\ &= 120 \cdot 719!. \end{aligned}

If nn were 720720 or more, then kn!720!,k \cdot n! \ge 720!, which exceeds 720!6.\frac{720!}{6}. So the largest possible value of nn is 719,719, achieved with k=120,k = 120, and k+n=120+719=839.k + n = 120 + 719 = 839.

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