How many ways can you arrange a deck of cards? - Yannay Khaikin
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Not SyncedPick a card, any card.
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Not SyncedActually, just pick up all of them and take a look.
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Not SyncedThis standard 52 card deck has been used for centuries.
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Not SyncedEveryday, thousands just like it
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Not Syncedare shuffled in casinos all over the world,
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Not Syncedthe order rearranged each time.
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Not SyncedAnd yet, every time you pick up a well shuffled deck
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Not Syncedlike this one,
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Not Syncedyou are almost certainly holding
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Not Syncedand arrangement of cards
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Not Syncedthat has never before existed in all of history.
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Not SyncedHow can this be?
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Not SyncedThe answer lies in how many different arrangements
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Not Syncedof 52 cards, or any objects, are possible.
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Not SyncedNow, 52 may not seem like such a high number,
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Not Syncedbut let's start with an even smaller one.
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Not SyncedSay we have four people trying to sit
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Not Syncedin four numbered chairs.
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Not SyncedHow many ways can they be seated?
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Not SyncedTo start off, any of the four people can sit
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Not Syncedin the first chair.
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Not SyncedOne this choice is made,
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Not Syncedonly three people remain standing.
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Not SyncedAfter the second person sits down,
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Not Syncedonly two people are left as candidates
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Not Syncedfor the third chair.
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Not SyncedAnd after the third person has sat down,
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Not Syncedthe last person standing has no choice
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Not Syncedbut to sit in the fourth chair.
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Not SyncedIf we manually write out all the possible arrangements,
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Not Syncedor permutations,
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Not Syncedit turns out that there are 24 ways
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Not Syncedthat four people can be seated in to four chairs,
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Not Syncedbut when dealing with larger numbers
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Not Syncedthis can take quite a while.
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Not SyncedSo let's see if there's a quicker way.
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Not SyncedGoing from the beginning again,
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Not Syncedyou can see that each of the four initial choices
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Not Syncedfor the first chair
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Not Syncedleads to three more possible choices for the second chair,
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Not Syncedand each of those choices
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Not Syncedleads to two more for the third chair,
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Not Syncedso instead of counting each final scenario individually,
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Not Syncedwe can multiply the number of choices for each chair:
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Not Syncedfour times three times two times one
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Not Syncedto achieve the same result of 24.
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Not SyncedAn interesting pattern emerges.
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Not SyncedWe start with the number of objects we're arranging,
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Not Syncedfour in this case,
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Not Syncedand multiply it by consecutively smaller integers
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Not Synceduntil we reach one.
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Not SyncedThis is an exciting discovery.
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Not SyncedSo exciting that mathematicians have chosen
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Not Syncedto symbolize this type of calculation,
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Not Syncedknown as a factorial,
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Not Syncedwith an exclamation mark.
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Not SyncedAs a general rule, the factorial of any positive integer
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Not Syncedis calculated as the product
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Not Syncedof that same integer
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Not Syncedand all smaller integers down to one.
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Not SyncedIn our simple example,
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Not Syncedthe number of ways four people
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Not Syncedcan be arranged in to chairs
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Not Syncedis written as four factorial,
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Not Syncedwhich equals 24.
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Not SyncedSo let's go back to our deck.
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Not SyncedJust as there were four factorial ways
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Not Syncedof arranging four people,
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Not Syncedthere are 52 factorial ways
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Not Syncedof arranging 52 cards.
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Not SyncedFortunately, we don't have to calculate this by hand.
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Not SyncedJust enter the function in to a calculator
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Not Syncedand it will show you that the number of
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Not Syncedpossible arrangements is
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Not Synced8.07 x 10^67,
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Not Syncedor roughly eight followed by 67 zeros.
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Not SyncedJust how big is this number?
- Title:
- How many ways can you arrange a deck of cards? - Yannay Khaikin
- Speaker:
- Yannay Khaikin
- Description:
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View full lesson: http://ed.ted.com/lessons/how-many-ways-can-you-arrange-a-deck-of-cards-yannay-khaikin
One deck. Fifty-two cards. How many arrangements? Let's put it this way: Any time you pick up a well shuffled deck, you are almost certainly holding an arrangement of cards that has never before existed and might not exist again. Yannay Khaikin explains how factorials allow us to pinpoint the exact (very large) number of permutations in a standard deck of cards.
Lesson by Yannay Khaikin, animation by The Moving Company Animation Studio.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 03:42
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Jennifer Cody edited English subtitles for How many ways can you arrange a deck of cards? |