This is a classic puzzle which can look simple.
Given 25 horses, find the best 3 horses with minimum number of races. Each race can have only 5 horses. You don't have a timer.
Now the challange is how we can do it in 7 races.
We will have 5 races with all 25 horses
Let the results be
Where a1 faster than a2 , a2 faster than a3 etc and
We need to consider only the following set of horses
We race a1,b1,c1,d1 abd e1
We get a1 as the fastest horse
We can ignore d1,d2,d3,e1,e2 and e3
Race a2,a3,b1,b2 and c1
The first and second will be second and third of the whole set