Three speed skaters race
Source: Canadian Mathematical Olympiad - 2010 - Problem 3.
May 6, 2011
floor functionalgebra unsolvedalgebra
Problem Statement
Three speed skaters have a friendly "race" on a skating oval. They all start from the same point and skate in the same direction, but with different speeds that they maintain throughout the race. The slowest skater does lap per minute, the fastest one does laps per minute, and the middle one does laps a minute for some . The race ends at the moment when all three skaters again come together to the same point on the oval (which may differ from the starting point.) Determine the number of different choices for such that exactly passings occur before the end of the race.
Note: A passing is defined as when one skater passes another one. The beginning and the end of the race when all three skaters are together are not counted as passings.