I do not know if I understood the question:

Rounds: 5 out of 25 horses will be chosen after 5 rounds.
Final: Taking the winner in each round, 5 will compete in final for 1, 2, 3rd spot.

we need just 6 total rounds .. Please correct me as none of the options match my outcome.

I think it should be 7

Remember we don't know times at which each horse completes the race. So its possible a 2nd place horse from Race-1 is faster than second place horse of Race-6.

(1-2-3-4-5) (6-7-8-9-10) (11-12-13-14-15) (16-17-18-19-20) (21-22-23-24-25)

Let these be the 25 horses.

Race 1 - 1 wins (2- 2nd position | 3 - 3rd position)
Race 2 - 6 wins (7 - 2nd position)
Race 3 - 11 wins (12 - 2nd position)
Race 4 - 16 wins ( 17 - 2nd position)
Race 5 - 21 wins (22 - 2nd position))

Race 6 (1-6-11-16-21)

Race 6 - 1 wins (say 6 comes 2nd and 11 comes 3rd)

So 1st - position is 1.

Now for 2nd and 3rd positions its possible 2 or 3 has a time < 6
(also) its possible 7 has time < than 11.

So Race 7 (2-3-6-7-11)

Now top 2 finishers will be 2nd and 3rd respectively.
Doesn't seem to be GMAT like problem, whats the source?

IMHO E

what is OA?

user123321

satishchandra wrote:On a race track a maximum of 5 horses can race together at a time. There are a total of 25 horses. There is no way of timing the races. What is the minimum number of races we need to conduct to get the top 3 fastest horses?
A. 5
B. 7
C. 8
D. 10
E. 11

Easier to see with a concrete example.

Round 1: 5 races, with the horses in descending order:
A-B-C-D-E
F-G-H-I-J
K-L-M-N-O
P-Q-R-S-T
U-V-W-X-Y
Winners are A, F, K, P, and U.

Round 2: 6th race, with the horses in descending order:
A-F-K-P-U.
The fastest horse of all is A.

F is faster than K.
Thus, if K is among the 3 fastest, then the 3 fastest will be A-F-K.
Thus, none of the horses L-Y can be among the 3 fastest.
But there are several horses against whom F and K still haven't raced.

F:
F still needs to race against B and C, who were top-3 finishers in Round 1, and could be faster than F.

K:
K still needs to race against B and C, who were top-3 finishers in Round 1, and could be faster than K.
K also has not yet raced against G or H, who also were top-3 finishers in Round 1.
But if G is among the 3 fastest horses, then the 3 fastest will be A-F-G, implying that H cannot be among the 3 fastest.
Thus, K still needs to race against G but not against H.

Round 3:
1 more race with F, K, B, C, and G.

Total number of races needed = 7.

The correct answer is B.

Mitch,

What about horses D, E. Won't F have to race against them as well ?
The same for K who will have to race against I, J ?

[email protected] wrote:Mitch,

What about horses D, E. Won't F have to race against them as well ?
The same for K who will have to race against I, J ?

D and E cannot be among the 3 fastest horses because they were beaten by A, B and C in round 1.
I and J cannot be among the 3 fastest horses because they were beaten by F, G and H in round 1.
Thus, there is no need to include D, E, I or J in any races after round 1.

Thanks Mitch.