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Rita and Sam play the following game with n sticks on a table. Each mu

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Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 03 Apr 2012, 13:02
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Rita and Sam play the following game with n sticks on a table. Each must remove 1, 2, 3, 4 or 5 sticks at a time on alternate turns, and no stick that is removed is put back on the table. The one who removes the last stick (or sticks) from the table wins. If Rita goes first, which of the following is a value of n such that Sam can always win no matter how Rita plays?

A. 7
B. 10
C. 11
D. 12
E. 16

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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 03 Apr 2012, 13:21
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eybrj2 wrote:
Rita and Sam play the following game with n sticks on a table. Each must remove 1,2,3,4, or 5 sticks at a time on alternate turns, and no stick that is removed is put back on the table. Tha one who removes the last stick (or sticks) from the table wins. If Rita goes first, which of the following is a value of n such that Sam can always win no matter how Rita plays?

A. 7
B. 10
C. 11
D. 12
E. 16


If the number of sticks on a table is a multiple of 6, then the second player will win in any case (well if the player is smart enough).

Consider n=6, no matter how many sticks will be removed by the first player (1, 2, 3 ,4 or 5), the rest (5, 4, 3, 2, or 1) can be removed by the second one.

The same for n=12: no matter how many sticks will be removed by the first player 1, 2, 3 ,4 or 5, the second one can remove 5, 4, 3, 2, or 1 so that to leave 6 sticks on the table and we are back to the case we discussed above.

Answer: D.
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 31 May 2013, 06:22
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 03 Jun 2013, 21:57
2
Bunuel wrote:
eybrj2 wrote:
Rita and Sam play the following game with n sticks on a table. Each must remove 1,2,3,4, or 5 sticks at a time on alternate turns, and no stick that is removed is put back on the table. Tha one who removes the last stick (or sticks) from the table wins. If Rita goes first, which of the following is a value of n such that Sam can always win no matter how Rita plays?

A. 7
B. 10
C. 11
D. 12
E. 16


If the number of sticks on a table is a multiple of 6, then the second player will win in any case (well if the player is smart enough).

Consider n=6, no matter how many sticks will be removed by the first player (1, 2, 3 ,4 or 5), the rest (5, 4, 3, 2, or 1) can be removed by the second one.

The same for n=12: no matter how many sticks will be removed by the first player 1, 2, 3 ,4 or 5, the second one can remove 5, 4, 3, 2, or 1 so that to leave 6 sticks on the table and we are back to the case we discussed above.

Answer: D.



Hi Bunnel,
Please explain this:

N = 12, here 1 and 2 shows steps in a game: rita picks 5 first, out of remaining 7 sam can pick a maximum of 5, which leaves 2 sticks after round one. On her next chance rita can pick 2 and win.

R S
1 5 5
2 2 > Rita wins

similarly:
R S
1 4 5
2 3 > Rita wins
R S
1 2 5
2 5 > Rita wins
R S
1 2 2
2 5 3 > Sam wins
R S
1 2 3
2 5 2 > Sam wins

So both can win when n=12.
I agree for n=6, but not for n=12.
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 04 Jun 2013, 03:46
1
cumulonimbus wrote:
Bunuel wrote:
eybrj2 wrote:
Rita and Sam play the following game with n sticks on a table. Each must remove 1,2,3,4, or 5 sticks at a time on alternate turns, and no stick that is removed is put back on the table. Tha one who removes the last stick (or sticks) from the table wins. If Rita goes first, which of the following is a value of n such that Sam can always win no matter how Rita plays?

A. 7
B. 10
C. 11
D. 12
E. 16


If the number of sticks on a table is a multiple of 6, then the second player will win in any case (well if the player is smart enough).

Consider n=6, no matter how many sticks will be removed by the first player (1, 2, 3 ,4 or 5), the rest (5, 4, 3, 2, or 1) can be removed by the second one.

The same for n=12: no matter how many sticks will be removed by the first player 1, 2, 3 ,4 or 5, the second one can remove 5, 4, 3, 2, or 1 so that to leave 6 sticks on the table and we are back to the case we discussed above.

Answer: D.



Hi Bunnel,
Please explain this:

N = 12, here 1 and 2 shows steps in a game: rita picks 5 first, out of remaining 7 sam can pick a maximum of 5, which leaves 2 sticks after round one. On her next chance rita can pick 2 and win.

R S
1 5 5
2 2 > Rita wins

similarly:
R S
1 4 5
2 3 > Rita wins
R S
1 2 5
2 5 > Rita wins
R S
1 2 2
2 5 3 > Sam wins
R S
1 2 3
2 5 2 > Sam wins

So both can win when n=12.
I agree for n=6, but not for n=12.


That;s not correct.

Both players can win BUT if the number of sticks on a table is a multiple of 6, then the second player will win in any case IF the player is smart enough.

n=12: no matter how many sticks will be removed by the first player 1, 2, 3 , 4 or 5, the second one can remove 5, 4, 3, 2, or 1, RESPECTIVELY so that to leave 6 sticks on the table.
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 04 Jun 2013, 19:12
If the number of sticks on a table is a multiple of 6, then the second player will win in any case (well if the player is smart enough).

Consider n=6, no matter how many sticks will be removed by the first player (1, 2, 3 ,4 or 5), the rest (5, 4, 3, 2, or 1) can be removed by the second one.

The same for n=12: no matter how many sticks will be removed by the first player 1, 2, 3 ,4 or 5, the second one can remove 5, 4, 3, 2, or 1 so that to leave 6 sticks on the table and we are back to the case we discussed above.

Answer: D.[/quote]


Hi Bunnel,
Please explain this:

N = 12, here 1 and 2 shows steps in a game: rita picks 5 first, out of remaining 7 sam can pick a maximum of 5, which leaves 2 sticks after round one. On her next chance rita can pick 2 and win.

R S
1 5 5
2 2 > Rita wins

similarly:
R S
1 4 5
2 3 > Rita wins
R S
1 2 5
2 5 > Rita wins
R S
1 2 2
2 5 3 > Sam wins
R S
1 2 3
2 5 2 > Sam wins

So both can win when n=12.
I agree for n=6, but not for n=12.[/quote]

That;s not correct.

Both players can win BUT if the number of sticks on a table is a multiple of 6, then the second player will win in any case IF the player is smart enough.

n=12: no matter how many sticks will be removed by the first player 1, 2, 3 , 4 or 5, the second one can remove 5, 4, 3, 2, or 1, RESPECTIVELY so that to leave 6 sticks on the table.[/quote]

got it. thanks.
is this gmat question ?
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 04 Jun 2013, 21:26
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eybrj2 wrote:
Rita and Sam play the following game with n sticks on a table. Each must remove 1,2,3,4, or 5 sticks at a time on alternate turns, and no stick that is removed is put back on the table. Tha one who removes the last stick (or sticks) from the table wins. If Rita goes first, which of the following is a value of n such that Sam can always win no matter how Rita plays?

A. 7
B. 10
C. 11
D. 12
E. 16


I would like to point out one thing about these questions based on games. These games are made to have a sure shot winner (if both players play intelligently and to win) under certain conditions. If A and B are playing, B's move will be decided by A's move if B has to win i.e. there are complementary moves. For example, in this question, if A picks 2 sticks, B must pick 4 sticks. If A picks 3 sticks, B must pick 3 too. So to solve these questions you need to find this particular complementary relation.

This question tell us that one can pick 1/2/3/4/5 sticks. This means n must be greater than 5 to have a game else the one who picks first will pick all and win. If n = 6, the first one to pick must pick at least 1 and at most 5 sticks leaving anywhere between 5 to 1 sticks for the other player. The other player will definitely win. If n= 7, the first player will pick 1 and leave the other player with 6 sticks. The first player will win. So the object of the game is to leave 6 sticks for your opponent. If the number of sticks is a multiple of 6, you can always make a complementary move to your opponent's move and ensure that you leave your opponent with 6 sticks. For example, if your opponent picks 1 stick, you pick 5, if he picks 2 sticks, you pick 4 and so on.

So when Rita starts, Sam can complement her move each time and leave her with 6 sticks at the end if the total number of sticks is a multiple of 6. There is only one multiple of 6 in the options.
Hence, answer must be (D)
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 02 Sep 2013, 21:05
so what is the generalisation in such questions or we just have to analyze everytime?
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 02 Sep 2013, 21:28
ygdrasil24 wrote:
so what is the generalisation in such questions or we just have to analyze everytime?


To have a sure shot winner, you need complimentary moves. You have to analyze to figure out the complimentary move every time, of course.
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 02 Sep 2013, 21:39
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ygdrasil24 wrote:
so what is the generalisation in such questions or we just have to analyze everytime?


The trick is to rephrase the question in more general terms. In this case it would be: What is the number that can always be divided into even number of times when each division can be up to 5. The answer is one greater than 5 which is 6 because whatever be the first value chosen, the second value can be chosen such that 6 can always be divided into two. The same idea can be extended to the multiples of 6 such that they can always be divided even number of times given that each division can be from 1 to 5.
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 23 Sep 2019, 00:07
Are 1,2,3,4,5 number on sticks or number of sticks?
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 23 Sep 2019, 00:10
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 23 Sep 2019, 00:13
cumulonimbus wrote:
Bunuel wrote:
eybrj2 wrote:
Rita and Sam play the following game with n sticks on a table. Each must remove 1,2,3,4, or 5 sticks at a time on alternate turns, and no stick that is removed is put back on the table. Tha one who removes the last stick (or sticks) from the table wins. If Rita goes first, which of the following is a value of n such that Sam can always win no matter how Rita plays?

A. 7
B. 10
C. 11
D. 12
E. 16


If the number of sticks on a table is a multiple of 6, then the second player will win in any case (well if the player is smart enough).

Consider n=6, no matter how many sticks will be removed by the first player (1, 2, 3 ,4 or 5), the rest (5, 4, 3, 2, or 1) can be removed by the second one.

The same for n=12: no matter how many sticks will be removed by the first player 1, 2, 3 ,4 or 5, the second one can remove 5, 4, 3, 2, or 1 so that to leave 6 sticks on the table and we are back to the case we discussed above.

Answer: D.



Hi Bunnel,
Please explain this:

N = 12, here 1 and 2 shows steps in a game: rita picks 5 first, out of remaining 7 sam can pick a maximum of 5, which leaves 2 sticks after round one. On her next chance rita can pick 2 and win.

R S
1 5 5
2 2 > Rita wins

similarly:
R S
1 4 5
2 3 > Rita wins
R S
1 2 5
2 5 > Rita wins
R S
1 2 2
2 5 3 > Sam wins
R S
1 2 3
2 5 2 > Sam wins

So both can win when n=12.
I agree for n=6, but not for n=12.


Exactly I was thinking, with 7 there are more probable cases when sam can win than with 12. And as such there is possibility he can win in any other game too if he can win with 12.
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 16 Oct 2019, 14:15
How would the following not happen?

n=12

R..S..R
4..3..5

Won't Rita win then?
Is it a must that each round of game play all the numbers (by removing that many sticks) 5,4,3,2,1?
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Re: Rita and Sam play the following game with n sticks on a table. Each mu  [#permalink]

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New post 16 Oct 2019, 14:30
Total number of the sticks must be a multiple of 6. If Rita removes n(<6) sticks in first turn, Sam will remove 6-n sticks in his first turn. This process can goes on until no stic remains on the table. Number of sticks remains after each turn of the Sam is a multiple of 6. Hence it's the Sam's turn after which there is no stick left on the table (as 0 is multiple of 6).




eybrj2 wrote:
Rita and Sam play the following game with n sticks on a table. Each must remove 1, 2, 3, 4 or 5 sticks at a time on alternate turns, and no stick that is removed is put back on the table. The one who removes the last stick (or sticks) from the table wins. If Rita goes first, which of the following is a value of n such that Sam can always win no matter how Rita plays?

A. 7
B. 10
C. 11
D. 12
E. 16

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Re: Rita and Sam play the following game with n sticks on a table. Each mu   [#permalink] 16 Oct 2019, 14:30
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