There are 25 horses and only 5 tracks. No of matches to find top 3 horses.

Problem:
There are 25 horses and only 5 tracks. So only 5 horses can run the race at a time. How many minimum no of races should be conducted to find the 3 best horses?
Sol: The answer is 7.
Round 1: Take 5 horses at a time. 5 winners of each race will go to round2.
Round 2: Winner of this will be top most horse.(call it W1)
Round 3: Final race comprises of following 5 horses.
h1: 2nd horse of round2
h2:3rd horse of round2
h3:2nd horse of W1's group during round 1
h4:3rd horse of W1's group during round1
h5:2nd horse of h1's group during round1