Riddle: 25 Horses
You have 25 horses. When they race, each horse runs at a different, constant pace. A horse will always run at the same pace no matter how many times it races.
You want to figure out which are your 3 fastest horses. You are allowed to race at most 5 horses against each other at a time. You don't have a stopwatch so all you can learn from each race is which order the horses finish in.
What is the least number of races you can conduct to figure out which 3 horses are fastest?
You can figure it out with 7 races. See if you can figure out how! A little hint: you can learn the most information about the most horses by first separating them into completely separate racing groups.