2012 USAJMO Problems/Problem 5
Contents
[hide]Problem
For distinct positive integers , , define to be the number of integers with such that the remainder when divided by 2012 is greater than that of divided by 2012. Let be the minimum value of , where and range over all pairs of distinct positive integers less than 2012. Determine .
Solution
The key insight in this problem is noticing that when is higher than , is lower than , except at residues*. Also, they must be equal many times. . We should have multiples of . After trying all three pairs and getting as our answer, we win. But look at the idea. What if we just took and plugged it in with ? We get .
--Va2010 11:12, 28 April 2012 (EDT)va2010
Alternate Solution
Say that the problem is a race track with spots. To intersect the most, we should get next to each other a lot so the negation is high. As , we intersect at a lot of multiples of .
See also
2012 USAJMO (Problems • Resources) | ||
Preceded by Problem 4 |
Followed by Problem 6 | |
1 • 2 • 3 • 4 • 5 • 6 | ||
All USAJMO Problems and Solutions |