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

Hat color problem--most asked question in interviews..

http://en.wikipedia.org/wiki/Prisoners_and_hats_puzzle

Two tribes one always tells true other false....

There were 2 tribes living on an island. The east tribal people always tell a lie. The west tribal people always tell the truth. Alan and Bryan came from the same tribe. However, we do not know which tribe they came from. When they were asked the marital status, Alan said: “Both of us are married.” But Bryan said: “I am not married”. Are they really married?


Ans:

Both are from same tribe. It means either both of them will lie or both will tell true. If we look at the statements both of them contradicts about Bryan's marital status. It means one of them is not telling truth, as they are from same tribe it concludes that they are from east tribe. It means Bryan is married and Alan's status is unclear.