This Mind-Bending 25 Horses Puzzle Was Asked at IIM Ahmedabad Interview— Can You Beat It?

Explain how to race 25 horses, 5 at a time, in the least number of races and determine the top 3.

Step 1: Divide and Race (5 races)
Divide 25 horses into 5 groups of 5 horses each:
Group A, B, C, D, E
Race each group once to determine their internal ranking.
That’s 5 races.
Let’s say results of each race are ordered fastest to slowest:

• Race 1 (Group A): A1 > A2 > A3 > A4 > A5
• Race 2 (Group B): B1 > B2 > B3 > B4 > B5
• Race 3 (Group C): C1 > C2 > C3 > C4 > C5
• Race 4 (Group D): D1 > D2 > D3 > D4 > D5
• Race 5 (Group E): E1 > E2 > E3 > E4 > E5

You now know relative speeds within groups, but not across.

Step 2: Race the Winners (1 race)
Now race the winners of each group:
A1, B1, C1, D1, E1
This is the 6th race.
Let’s assume the result is:
A1 > B1 > C1 > D1 > E1
This tells us that:

• A1 is the fastest overall
• B1 could be 2nd or 3rd
• C1 might still have a shot at 3rd
• D1 and E1 can be eliminated from top 3 contention

Step 3: Final Race (7th race)
Now, from remaining contenders, select those who could still be in top 3:<br/ >

• A2, A3 (2nd and 3rd in the winning group)
• B1, B2 (1st and 2nd in 2nd place group)
• C1 (1st in 3rd place group)

Race these 5 horses: A2, A3, B1, B2, C1
This is the 7th and final race
Assume result is: B1 > A2 > C1 > B2 > A3

You can finally determine the top 3 fastest horses in just 7 races.

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