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Interview Brain Teasers Hard 5 min

You have 25 horses and can race only 5 horses at a time. There is no stopwatch; you only know the finishing order in each race. What is the minimum number of races needed to determine the three fastest horses?

Hint
First establish rankings within groups, then compare the group winners.

Answer

7 races.

Explanation

Race the 25 horses in five groups, requiring 5 races. Race the five winners in race 6. The winner of that race is fastest overall. A final race among the only remaining candidates can determine second and third.

Step-by-Step Solution

Five preliminary races = 5.
Race the five winners = 1.
A final comparison among the remaining candidates = 1.
Total = 7.
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