A Tennis Tournament

There are 100 players in a tennis tournament. The tournament is single-elimination, meaning that if a player loses a match, he or she is out of the tournament. How many matches must be played before the winner is determined?


The answer is 99.

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12 solutions

Michael Tang
Dec 23, 2013

At the end of the match, there is only one winner, meaning that there are 99 99 losers. Since each match determines exactly one loser, there must be exactly 99 \boxed{99} matches.

Extension: Consider a game with 2 n 2^n people, for some positive integer n . n. Use the clever method above, and also count directly, to find the number of games played, and therefore to get a combinatorical proof of the identity

1 + 2 + 4 + + 2 n 1 = 2 n 1. 1 + 2 + 4 + \ldots + 2^{n-1} = 2^n - 1.

Michael Tang - 7 years, 5 months ago

100-1=99

Sälmän Rähmän - 7 years, 4 months ago

Michael tang is too complicated

Joe Bob - 7 years, 4 months ago

Same method yet another way of thinking. The question has a direct application of pigeon-hole theorem

Tilak Patel - 7 years, 5 months ago

Log in to reply

PIGEON-HOLE Theorem????

Priyansh Agrawal - 7 years, 5 months ago

solve this: The function f(x) satisfies the equation f(x) = f(x−1)+f(x+1) for all values of x. If f(1) =1 and f(2) = 3, what is the value of f(2013)?

Sälmän Rähmän - 7 years, 4 months ago
Milly Choochoo
Dec 23, 2013

You sort of have to read this twice to understand it.

So every time you have a number of competitors, you must divide it in half in order to see how many players will be left over. You can think of this by using simple numbers like 4 4 or 6 6 . What you'll find by doing that is that the number of competitors remaining after all of those 1 v 1 matches is the also the number of matches that took place. So if there were 4 4 competitors, there would be 2 2 matches before the second round started. So this is how I did it...

100 2 = 50 \frac{100}{2} = 50

50 2 = 25 \frac{50}{2} = 25

Now here's the tricky part. We have an odd number of players, so how do we go about dividing it? This is where reading the problem again helps. If there are only 1 v 1 matches, and anybody who loses is out of the tournament , then you can just take out one of the contestants and sit them off to the side. Think of that contestant being in a sort of waiting line.

Now we can continue...

25 1 = 24 25 - 1 = 24

24 2 = 12 \frac{24}{2} = 12

12 2 = 6 \frac{12}{2} = 6

6 2 = 3 \frac{6}{2} = 3

Now here's the last tricky part. We have three players left. That's an odd number, so we can just take that player that we put in the waiting line, and throw him in there. Now if we do the simple math, we will find that there will be 3 3 matches between those 4 4 players before the winner is determined. So now we can just simply add up the number of matches!

50 + 25 + 12 + 6 + 3 + 3 = 99 50 + 25 + 12 + 6 + 3 + 3 = \boxed{99 }

So there will be 99 99 matches before the winner is determined from those 100 100 competitors.

did the same way..

Priyesh Pandey - 7 years, 5 months ago

That's way too much work for this simple problem

Joe Bob - 7 years, 4 months ago

did the same way ,but concluded wrong

Apurv Rajput - 7 years, 2 months ago

the first method is a really clever one nd simpler the solutions better is the understanding of it

Aditya Pandey - 7 years, 2 months ago

my god..........ki kasam.........

Nikhil Jha - 7 years, 1 month ago
Ajinkya Bokade
Dec 23, 2013

THERE ARE 100 PLAYERS. WE HAVE TO CALCULATE THE NUMBER OF MATCHES BEFORE THE WINNER IS DETERMINED. IF FIRST MATCH IS PLAYED BETWEEN ANY TWO PLAYERS, THEN ONE WOULD BE WINNER AND ANOTHER WOULD BE LOSER. THE LOSER WILL BE ELIMINATED. THEREFORE FROM THE TOTAL NUMBER OF PLAYERS, 1 WOULD BE ELIMINATED OR SUBTRACTED. FOR ANY MATCH TO BE PLAYED BETWEEN TWO PLAYERS, ONE WOULD BE ALWAYS ELIMINATED. THEREFORE FOR N PLAYERS, N-1 MATCHES WOULD BE REQUIRED BEFORE THE WINNER IS DETERMINED. THEREFORE FOR 100 PLAYERS, 100-1=99 MATCHES WOULD BE REQUIRED BEFORE THE WINNER IS DETERMINED. ANS:-\BOXED{99}

Your solution is well explained, just lose the caps lock. As this makes it difficult to read.

Peter Michael - 7 years, 5 months ago

thanks!

AJINKYA BOKADE - 7 years, 5 months ago

Nice explanation . It should be like 99 \boxed{99} . just see formatting guide .

Devesh Rai - 7 years, 5 months ago
Budi Utomo
Dec 23, 2013

With technical meeting usually, an organization had processed that 100 ----- (50)----- 50 ------(25)------25 ---> 25 = 16 + 9. Then, 16------(8)-----8-----(4)-------4 --------(2)--------(1)------1 ; 9 = 8 + 1 ----> 8 ----- (5)-----4----(2)----2------(1)-----1 , (1). So, matches must be played before the winner is determined is (50)+(25)+(8)+(4)+(2)+(1)+(5)+(2)+(1)+(1) = 99. Answer : 99.

what denotion is this.

Sunil Nandella - 7 years, 4 months ago
Chandra Shekar
Feb 26, 2014

100-1=99

Joe Bob
Feb 11, 2014

It's obvious

Robin Leach
Feb 5, 2014

You have 100 players, and 1 is knocked out per match leaving one winner, ergo you must have 99 matches to knock out the 99 losers.

Yash Bhagwat
Feb 2, 2014

50+25+12+6+3+2+1=99

Bilal Ayub
Jan 17, 2014

After 50 matches between 100 players, 50 will remain. After 25 more matches between 50 players, 25 will remain. After 12 more matches between 24 players, 12 will remain plus one player who haven't played a match yet. After 6 more matches between 12 players, 6 will remain. After 3 matches between 6 players, 3 will remain. The played without a match will come in to play. After 2 matches between 4 players, 2 will remain. and the Final one Match from which one will be a winner.

50+25+12+6+3+2+1 =99

the formula os single tournament is n-1. so 100-1 = 99.

Rizky Riman
Jan 10, 2014

100-1 = 99 If there is a third place, use 100-1+1

Mahiuddin Rasel
Jan 6, 2014

Here is 100 player and the tournament has single-elimination so we ensure that first round has 100/2=50 match.Second round has 50/2=25 match.Third round has 25/2=12+1 match.Fourth round has 12/2=6 match.Fifth round has 6/2=3 match. sixth round has 3/2=1+1 match, So total number of match is 50+25+(12+1)+6+3+(1+1)=99

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