The three fastest horses:
A horse farmer takes you to his track and asks you to find the 3 fastest horses out of the 25 he owns. There are three parameters/givens to this test:
- Regardless of how many times you run them, the horses are relatively consistent - meaning if horse "A" is faster than horse "B" in one race, he is ALWAYS faster than Horse "B".
- You can't use a stop watch
- You can only race five horses at a time on the track.
What is the minimum number of races you need to run to find horses 1,2, and 3, and how do you set them up?
@yitzgar @etech0 @aygart @Definitions you guys are on the right track.
The answer is 7 - and here is why:
You group them in groups of 5, and Run 5 different races - let's call the groups A,B,C,D,E; and within their groups as 1-5; So A1 is the fastest horse in group A and A5 is the slowest.
In the 6th race, you run all of the first place horses, let's say that the Order of the 6th race is A1,B1,C1,D1,E1
After race 6, given that they're all relatively consistent speed was, you know the following:
- A1 is the fastest horse
- All of the horses in Groups D and E are out
- A2 and A3 might be the 2nd and 3rd fastest, but A4 and A5 are out
- B1 and B2 might be the 2nd and 3rd fastest, but B3,4,5 are out (since B1 can be 2nd at best, B3 can be 4th at best)
- C1 could be third at best - C2-5 are out.
So 2nd and 3rd place have 5 remaining horses:
A2, A3, B1,B2,C1
And they race to determine the places.