A total of 512 players participated in a single tennis knock : GMAT Problem Solving (PS)
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# A total of 512 players participated in a single tennis knock

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A total of 512 players participated in a single tennis knock [#permalink]

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01 May 2012, 20:26
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A total of 512 players participated in a single tennis knock out tournament. What is the total number of matches played in the tournament? (Knockout means if a player loses, he is out of the tournament). No match ends in a tie.

A. 511
B. 512
C. 256
D. 255
E. 1023

I chose D, solved this way - after first 256 matches, remaing players 256 (those 256 who lost are knocked out), after another 128 matches, remaining players are 128, after 64 more matches, no of remainig players are 64, after 32, 32, after 16, 16, after 8, 8, after 4, 4, after 2,2, and then 1 -
total 256 + 128+64+32+16+8+1 = 255 matches

However, the correct answer given is A 511, can anyone please exlain what's wrong in my approach? Thanks!
[Reveal] Spoiler: OA
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Re: A total of 512 players participated in a single tennis knock [#permalink]

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19 Nov 2012, 18:17
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There are 512 players, only 1 person wins, 511 players lose. in order to lose, you must have lost a game.

511 games.
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Re: A total of 512 players participated in a single tennis knock [#permalink]

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01 May 2012, 22:00
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Expert's post
gmihir wrote:
A total of 512 players participated in a single tennis knock out tournament. What is the total number of matches played in the tournament? (Knockout means if a player loses, he is out of the tournament). No match ends in a tie.

A. 511
B. 512
C. 256
D. 255
E. 1023

I chose D, solved this way - after first 256 matches, remaing players 256 (those 256 who lost are knocked out), after another 128 matches, remaining players are 128, after 64 more matches, no of remainig players are 64, after 32, 32, after 16, 16, after 8, 8, after 4, 4, after 2,2, and then 1 -
total 256 + 128+64+32+16+8+1 = 255 matches

However, the correct answer given is A 511, can anyone please exlain what's wrong in my approach? Thanks!

You've done everything right except calculation: 256+128+64+32+16+8+4+2+1=511.

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Re: A total of 512 players participated in a single tennis knock [#permalink]

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26 Feb 2013, 18:12
1- the 512 players will play 256 games --> 256 plyers will go out from these games
2- the remaining is 256 players, they will play 128 games --> 128 players will go out
3- the remaining is 128 players, they will play 64 games --> 64 players will go out
4- the remaining is 64 players, they will play 32 games --> 32 players will go out
5- the remaining is 32 players, they will play 16 games --> 16 players will go out
6- the remaining is 16 players, they will play 8 games --> 8 players will go out
7- the remaining is 8 players, they will play 4 games --> 4 players will go out
8- the remaining is 4 players, they will play 2 games --> 2 players will go out.
9- the remaining is 2 players, they will play 1 games --> 1 players will go out

265+128+64+32+16+8+4+2+1=511
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Re: A total of 512 players participated in a single tennis knock [#permalink]

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27 Feb 2013, 11:44
AlyoshaKaramazov wrote:
There are 512 players, only 1 person wins, 511 players lose. in order to lose, you must have lost a game.

511 games.

I know this is an old post. But damn, sometimes the answer is so simple, you just have to thinkg logically.

Thanks Alyosha
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Re: A total of 512 players participated in a single tennis knock [#permalink]

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24 Jun 2013, 07:23
If you divide 512 by 2 recursively to factor: 512,256,128,64,32,16,8,4,2,1. so the answer narrows to down to either A or B.
Since the last dividend is 1, the sum will be odd so it should be 511

A
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Re: A total of 512 players participated in a single tennis knock [#permalink]

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26 Dec 2013, 12:05
Bunuel wrote:
gmihir wrote:
A total of 512 players participated in a single tennis knock out tournament. What is the total number of matches played in the tournament? (Knockout means if a player loses, he is out of the tournament). No match ends in a tie.

A. 511
B. 512
C. 256
D. 255
E. 1023

I chose D, solved this way - after first 256 matches, remaing players 256 (those 256 who lost are knocked out), after another 128 matches, remaining players are 128, after 64 more matches, no of remainig players are 64, after 32, 32, after 16, 16, after 8, 8, after 4, 4, after 2,2, and then 1 -
total 256 + 128+64+32+16+8+1 = 255 matches

However, the correct answer given is A 511, can anyone please exlain what's wrong in my approach? Thanks!

You've done everything right except calculation: 256+128+64+32+16+8+4+2+1=511.

Geometric progression

512 = 2^9

2^1 + 2^2 ....+2^9 + 1

2 ( 2^8-1) = 2^9 - 2 + 1

A is our friend here

Cheers!
J
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Re: A total of 512 players participated in a single tennis knock [#permalink]

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03 Jan 2014, 16:34
gmihir wrote:
A total of 512 players participated in a single tennis knock out tournament. What is the total number of matches played in the tournament? (Knockout means if a player loses, he is out of the tournament). No match ends in a tie.

A. 511
B. 512
C. 256
D. 255
E. 1023

I chose D, solved this way - after first 256 matches, remaing players 256 (those 256 who lost are knocked out), after another 128 matches, remaining players are 128, after 64 more matches, no of remainig players are 64, after 32, 32, after 16, 16, after 8, 8, after 4, 4, after 2,2, and then 1 -
total 256 + 128+64+32+16+8+1 = 255 matches

However, the correct answer given is A 511, can anyone please exlain what's wrong in my approach? Thanks!

256+128+ 64+32+16+8+4+2+1
= 511
OA - A

Thanks for posting

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Re: A total of 512 players participated in a single tennis knock [#permalink]

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20 Apr 2015, 03:47
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A total of 512 players participated in a single tennis knock [#permalink]

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25 Jun 2015, 01:14
One of the best logics I've seen for these knockout questions is as follows:

In this question, there are 512 participants. And it takes ONE match to eliminate ONE player. So at the end of the day you need to eliminate everyone except the winner. ie. you need to eliminate 511 participants and naturally you need 511 matches for the same
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Re: A total of 512 players participated in a single tennis knock [#permalink]

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18 Apr 2016, 00:13
gmihir wrote:
A total of 512 players participated in a single tennis knock out tournament. What is the total number of matches played in the tournament? (Knockout means if a player loses, he is out of the tournament). No match ends in a tie.

A. 511
B. 512
C. 256
D. 255
E. 1023

I chose D, solved this way - after first 256 matches, remaing players 256 (those 256 who lost are knocked out), after another 128 matches, remaining players are 128, after 64 more matches, no of remainig players are 64, after 32, 32, after 16, 16, after 8, 8, after 4, 4, after 2,2, and then 1 -
total 256 + 128+64+32+16+8+1 = 255 matches

However, the correct answer given is A 511, can anyone please exlain what's wrong in my approach? Thanks!

If there are 2 players, then there will be only 1 match
If there are 4 players, then there will be 2+1 matches
8 players, 4+2+1=7
16 players, 8+4+2+1 = 15
Now you are getting the pattern
512 players, 256+128+64+..+2+1=511
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Re: A total of 512 players participated in a single tennis knock [#permalink]

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18 Apr 2016, 11:01
Mathivanan Palraj wrote:
gmihir wrote:
A total of 512 players participated in a single tennis knock out tournament. What is the total number of matches played in the tournament? (Knockout means if a player loses, he is out of the tournament). No match ends in a tie.

A. 511
B. 512
C. 256
D. 255
E. 1023

I chose D, solved this way - after first 256 matches, remaing players 256 (those 256 who lost are knocked out), after another 128 matches, remaining players are 128, after 64 more matches, no of remainig players are 64, after 32, 32, after 16, 16, after 8, 8, after 4, 4, after 2,2, and then 1 -
total 256 + 128+64+32+16+8+1 = 255 matches

However, the correct answer given is A 511, can anyone please exlain what's wrong in my approach? Thanks!

If there are 2 players, then there will be only 1 match
If there are 4 players, then there will be 2+1 matches
8 players, 4+2+1=7
16 players, 8+4+2+1 = 15
Now you are getting the pattern
512 players, 256+128+64+..+2+1=511

Good catch , or U can go the other way round -

When there are 2 player only 1 knockout match is needed
When there are 3 player only 2 knockout match is needed
When there are 4 player only 3 knockout match is needed

So, the pattern formed is -

When there are n player only n - 1 knockout match is needed

Hence , When there are 512 player only 511 (512 - 1 ) knockout match is needed

Either way answer will be the same but the best thing/strategy is to solve the problems within minimum time & calculation
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Re: A total of 512 players participated in a single tennis knock [#permalink]

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22 Apr 2016, 13:59
Firstly the question should state that a match is played between 2 players (what if its a cricket match)
assuming the match is played between 2 teams = > number of matches => 512/2 + 256/2 +128/2+64/2+32/2+16/2+8/2+4/2+2/2
we dont need to calculate the sum here => the unit digit will be 1
SMASH that A
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Re: A total of 512 players participated in a single tennis knock [#permalink]

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31 Aug 2016, 09:54
stonecold wrote:
Firstly the question should state that a match is played between 2 players (what if its a cricket match)
assuming the match is played between 2 teams = > number of matches => 512/2 + 256/2 +128/2+64/2+32/2+16/2+8/2+4/2+2/2
we dont need to calculate the sum here => the unit digit will be 1
SMASH that A

1. Question mentions that it is a Tennis Tournament of Singles.
2. All we know is that the sum is Odd. Please explain how will you get the unit's digit = 1 by looking at the sequence.

My Solution:

# of matches = 256 + 128 + 64 + ... + 2 + 1 = $$2^8 + 2^7 + 2^6 + ... + 2^1 + 2^0$$ => Ascending G.P.

Sum of G.P. =$$\frac{a(r^n - 1)}{a-1}$$
Where,
a = First Term = 1 (Sum starts from 1)
r = Common Ratio = 2 (ratio of each successive term is 2)
n = Number of terms = 9

Therefore,
Sum = $$\frac{1 * (2^9 - 1)}{2-1}$$ = 512 - 1 = 511
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Re: A total of 512 players participated in a single tennis knock   [#permalink] 31 Aug 2016, 09:54
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