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24
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A standard deck of cards contains  52 cards. These 52  cards are arranged in a circle, at random. Find the expected number of pairs of adjacent cards that are both Aces.

 Feb 6, 2024
edited by UniCorns555  Feb 6, 2024
 #1
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2. When the set of natural numbers is listed in ascending order, what is the smallest prime number that occurs after a sequence of five consecutive positive integers all of which are non prime?

 Feb 6, 2024
 #2
avatar+129881 
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2. When the set of natural numbers is listed in ascending order, what is the smallest prime number that occurs after a sequence of five consecutive positive integers all of which are non prime?

 

24,25,26,27,28

 

Smallest prime  = 29

 

cool cool cool

 Feb 6, 2024
 #3
avatar+297 
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I'll try my best on this one, I'm not particularly good with this topic.

 

So the first Ace can appear anywhere, so 52 choices, times 4 since it could be any of the 4 aces.

The ace adjacent to it has 2 choices, left or right, and has 3 choices on which type of ace.

 

The probability of this happening is \(\frac{52\cdot4\cdot2\cdot3}{52\cdot52\cdot2\cdot51}\) which will end up being \(\frac{1}{221}\)

 

so the expected number of times is 0.

 Feb 6, 2024
 #5
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the correct answer was 4/17 The number of pairs of adjacent cards which are both Aces is equal to the number of Aces which have another Ace to their right. For each Ace, there is a 3/51 chance that the card to its right is also an Ace, giving 1 pair, and a 48/51 chance that the card to its right is not an Ace, giving 0 pairs. There are four Aces, so the expected value of the number of pairs of cards that are both Aces is \[4\left(\frac{3}{51}(1)+\frac{48}{51}(0)\right) = \frac{12}{51} = \boxed{\frac{4}{17}}.\]
UniCorns555  Feb 8, 2024

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