A Game of cards with Mr. 11 ...

Satvik and Krishna are playing a game of cards. Both of them are holding one card in hand chosen from the deck . It's given that the number on Krishna's card is strictly greater than the number on Satvik's card.

The number of ways in which this can happen is K K .

Find the remainder when K K is divided by 11 11 .


Details and assumptions :-

1. 1.\quad A deck of card has 52 cards, which are divided into 4 suits (Hearts \color{#D61F06}{❤} ,Diamonds \color{#D61F06}{♦} ,Club \clubsuit ,Spade \spadesuit ). Each suit has 13 cards, which are { Ace ,2,3,4,5,6,7,8,9,10, Jack,Queen,King }.

2. 2.\quad In this question, consider that the numbers assigned to cards are Ace=1,Jack=11,Queen=12,King=13 \text{Ace=1,Jack=11,Queen=12,King=13} and others are numbered as they are already.


This problem is a part of the set 11≡ awesome (mod remainders)


The answer is 5.

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4 solutions

Number of ways in which I can pick two cards and distribute between Krishna and Satvik = ( 52 2 ) 2 ! = {52 \choose 2} 2!

Number of ways in which the cards can be of equal value = 13 ( 4 2 ) 2 ! = 13 {4 \choose 2} 2!

So, number of ways the cards can be chosen so that the distribution is unequal = ( 52 2 ) 2 ! 13 ( 4 2 ) 2 ! = {52 \choose 2} 2! - 13 {4 \choose 2} 2!

Now, for every distribution where Satvik gets a card greater than Krishna, there exists a distribution consisting of the same cards such that Krishna is greater than Satvik, just by switching the cards.

So, half of the time, Krishna's card is greater than Satvik's

So, required number of ways = 1 2 ( ( 52 2 ) 2 ! 13 ( 4 2 ) 2 ! ) = \frac{1}{2}\left ( {52 \choose 2} 2! - 13 {4 \choose 2} 2! \right )

Evaluating it gives 1248 1248

The answer is 1248 ( m o d 11 ) = 5 1248 \pmod{11} = \boxed{5}

This had come to my mind, but I felt that the one i posted is bit more elegant, but this is also., none less than awesome .

Aditya Raut - 6 years, 8 months ago
Aditya Raut
Sep 22, 2014

Let's say that for ease, Satvik has card of \spadesuit . Then there are 13 13 choices for his card.

For each card, Krishna will have a card greater than that number, being of any suit (4 choices of suits).

img img See the the number of ways in which this happens is

48 + 44 + 40 + . . . + 4 = 4 × ( 1 + 2 + 3 + . . . + 12 ) = 4 × 12 × 13 2 = 312 48+44+40+...+4\\ =4\times (1+2+3+...+12) \\= 4\times \dfrac{12\times 13}{2} \\ = \quad\mathbf{312}


This was for 1 1 suit of Satvik, so for all 4 4 suits , there will be 312 × 4 = 1248 312\times 4=1248 ways.


Thus, answer = 1248 ( m o d 11 ) = 5 1248 \pmod{11} = \boxed{5}

Great problem, Better solution

Sualeh Asif - 6 years, 8 months ago

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And how's the name ?

A Game of cards with Mr. 11 \textbf{A Game of cards with Mr. 11} ?

Aditya Raut - 6 years, 8 months ago

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Better titles than what you usually have These kind of problems get me going mad about mathematics

Sualeh Asif - 6 years, 8 months ago

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@Sualeh Asif loooooooool same with me

math man - 6 years, 8 months ago

Beautiful and awesome!!!

Adarsh Kumar - 6 years, 8 months ago

@Krishna Ar and @Satvik Golechha might be happy (?) to see their names...

Aditya Raut - 6 years, 8 months ago

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@Aditya Raut Super-Duper-Cool.. :D I love the way you use brilliantians in your problems.. CJ, Krishh, then me!!

Satvik Golechha - 6 years, 8 months ago

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Better word's friends rather than brillliantians, because I don't name all of them...

Aditya Raut - 6 years, 8 months ago

And I thought it was me -_-

Krishna Sharma - 6 years, 8 months ago

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Ok, it's you also !

Aditya Raut - 6 years, 8 months ago

Wow! Finally, I solved it! Thanks :P

Krishna Ar - 6 years, 8 months ago

i just forgot to multiply 4 to 312

Vighnesh Raut - 6 years, 8 months ago

I have a simpler solution except it does not provide a way to calculate 1248 mod 11

Agnishom Chattopadhyay - 6 years, 8 months ago

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Please post it

Sualeh Asif - 6 years, 8 months ago

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I just posted it. Please check it out

Agnishom Chattopadhyay - 6 years, 8 months ago

@Aditya Raut What is your favorite prime?

Agnishom Chattopadhyay - 6 years, 8 months ago

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My favorite prime is

Optimus Prime \Huge{\textbf{Optimus Prime}}

Aditya Raut - 6 years, 8 months ago

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What else could you expect from a friend of the King of Trolls and the Founder of Healthy Trollism?

Satvik Golechha - 6 years, 8 months ago

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@Satvik Golechha And why do I expect FALSE COLORS effect to the Horse Power ? अश्व शक्ती ...

Aditya Raut - 6 years, 8 months ago

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@Aditya Raut I Thought the new blazing colour is more cooler.

Satvik Golechha - 6 years, 8 months ago

LOL (ROTFL)

Krishna Ar - 6 years, 8 months ago

I'm sure these people will be interested in knowing this answer... @Krishna Ar @Satvik Golechha

Aditya Raut - 6 years, 8 months ago
Rayner Chuang
Oct 6, 2014

Firstly, there is are 52 × 51 52\times 51 ways for Satvik and Krishna to choose cards. For any card that Krishna has, there is a 3 51 \frac { 3 }{ 51 } chance for Satvik to have a card of the same value.

Then, notice that the chance of Krishna having a card strictly greater than Satvik's must be the same as the chance of Satvik having a card strictly greater than Satvik's card, with the probability of both events happening being ( 1 3 51 ) ( 1 2 ) = 24 51 (1-\frac { 3 }{ 51 } )(\frac { 1 }{ 2 } )=\frac { 24 }{ 51 } .

By multiplying the probability to the number of ways for cards to be picked, we get the following:

K = 24 51 × 51 × 52 = 24 × 52 2 × 8 5 ( m o d 11 ) K\quad =\quad \frac { 24 }{ 51 } \times \quad 51\quad \times \quad 52\\ \qquad =\quad 24\quad \times \quad 52\\ \qquad \equiv \quad 2\quad \times \quad 8\\ \qquad \equiv \quad \boxed{ 5 } \quad (mod\quad 11)

Jp Delavin
Sep 24, 2014

Let k k be the number on Krishna's card. We know that there are 4 ways of getting a card with a value k k .

Since Krishna's card is higher than Satvik's, k k cannot have a value of 1 1 . The number of cards lower than k k is 4 ( k 1 ) 4(k-1) . Given these, the number of ways in which Krishna's card is greater than Satvik's is:

k = 2 13 4 ( 4 ) ( k 1 ) \sum\limits_{k=2}^{13} 4(4)(k-1)

= 16 k = 2 13 k 1 =16\sum\limits_{k=2}^{13} k-1

= 16 i = 1 12 i =16\sum\limits_{i=1}^{12} i

= 16 ( 12 ) ( 12 + 1 ) 2 = 1248 =\frac{16(12)(12+1)}{2}=1248

1248 5 m o d 11 1248 \equiv 5\mod 11

you gise are poop

Elliot Fujimoto - 1 year, 9 months ago

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you guys are poop poop

Elliot Fujimoto - 1 year, 9 months ago

you guys are are convusenen me

Elliot Fujimoto - 1 year, 9 months ago

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