2002 AIME II Problem 8

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Concepts:floor and ceiling functionscounting integers in a range

Difficulty rating: 2560

8.

Find the least positive integer kk for which the equation 2002n=k\left\lfloor \frac{2002}{n} \right\rfloor = k has no integer solutions for n.n. (The notation x\lfloor x \rfloor means the greatest integer less than or equal to x.x.)

Solution:

The value kk is attained exactly when some integer nn satisfies k2002n<k+1,k \le \frac{2002}{n} \lt k + 1, that is, when the interval (2002k+1,2002k]\left(\frac{2002}{k+1}, \frac{2002}{k}\right] contains an integer. Its length is 2002k(k+1),\frac{2002}{k(k+1)}, which is at least 11 whenever k(k+1)2002k(k+1) \le 2002 — so every k44k \le 44 is attained.

For larger k,k, check directly: n=44,43,42,41,40n = 44, 43, 42, 41, 40 give 2002n=45,46,47,48,50.\left\lfloor \frac{2002}{n} \right\rfloor = 45, 46, 47, 48, 50. Since 20024148.8\frac{2002}{41} \approx 48.8 and 200240>50,\frac{2002}{40} \gt 50, the value 4949 is never attained, so the least such kk is 49.49.

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