Can you solve the fantasy election riddle? - Dennis E. Shasha

1,661,115 views ใƒป 2021-03-25

TED-Ed


ืื ื ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ืœืžื˜ื” ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ.

ืชืจื’ื•ื: Ido Dekkers ืขืจื™ื›ื”: zeeva livshitz
00:06
After much debate, the fantasy realm you call home
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ืื—ืจื™ ื”ืจื‘ื” ื“ื™ื•ื ื™ื, ืžืžืœื›ืช ื”ืคื ื˜ื–ื™ื” ืฉืืชื ืงื•ืจืื™ื ืœื” ื‘ื™ืช
00:10
has decided dragon jousting may not be the best way to choose its leaders,
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ื”ื—ืœื™ื˜ื” ืฉืžืœื—ืžื” ื‘ื“ืจืงื•ื ื™ื ื”ื™ื ืื•ืœื™ ืœื ื”ื“ืจืš ื”ื›ื™ ื˜ื•ื‘ื” ืœื‘ื—ื•ืจ ืžื ื”ื™ื’,
00:15
and has begun transitioning to democracy.
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ื•ื”ื—ืœื” ืœืขื‘ื•ืจ ืœื“ืžื•ืงืจื˜ื™ื”.
00:18
The candidates are a giant orange troll and an experienced tree statesman.
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ื”ืžื•ืขืžื“ื™ื ื”ื ื˜ืจื•ืœ ื›ืชื•ื ืขื ืง ื•ืžื“ื™ื ืื™ ืขืฅ ืžื ื•ืกื”.
00:24
An all-powerful eyebrow has hired your companyโ€” The Dormor Polling Agencyโ€”
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ื’ื‘ื” ื‘ืขืœืช ื›ื•ื— ืขืœ ืฉื›ืจื” ืืช ื—ื‘ืจืชื›ื -- ื—ื‘ืจืช ื”ืกืงืจื™ื ื“ื•ืจืžื•ืจ --
00:30
to survey the citizens of the land and predict who will win.
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ื›ื“ื™ ืœืกืงื•ืจ ืืช ื”ืื–ืจื—ื™ื ื•ืœื—ื–ื•ืช ืžื™ ื™ื–ื›ื”.
00:33
Thereโ€™s a lot riding on this:
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ื”ืจื‘ื” ื“ื‘ืจื™ื ืชืœื•ื™ื™ื ื‘ื–ื”:
00:36
if you get it wrong, headsโ€” well, your headโ€”
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ืื ืชื˜ืขื•, ืจืืฉื™ื -- ื•ื‘ื›ืŸ, ื”ืจืืฉ ืฉืœื›ื --
00:39
will quite literally roll.
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ื™ืชื’ืœื’ืœ ืžื™ืœื•ืœื™ืช.
00:41
Your job is to go from door to door,
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ื”ืขื‘ื•ื“ื” ืฉืœื›ื ื”ื™ื ืœืขื‘ื•ืจ ืžื“ืœืช ืœื“ืœืช,
00:44
asking voters whether they prefer the troll or the treefellow
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ื•ืœืฉืื•ืœ ื‘ื•ื—ืจื™ื ืื ื”ื ืžืขื“ื™ืคื™ื ืืช ื”ื˜ืจื•ืœ ืื• ืื™ืฉ ื”ืขืฆื™ื
00:48
and to use the results to project how the election will go.
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ื•ืœื”ืฉืชืžืฉ ื‘ืชื•ืฆืื•ืช ื›ื“ื™ ืœื—ื–ื•ืช ืืช ืชื•ืฆืื•ืช ื”ื‘ื—ื™ืจื•ืช.
00:53
Your fellow citizens want you to succeed and would tell you the truth...
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ืขืžื™ืชื™ื›ื ื”ืื–ืจื—ื™ื ืจื•ืฆื™ื ืฉืชืฆืœื™ื—ื• ื•ื™ื’ื™ื“ื• ืœื›ื ืืช ื”ืืžืช...
00:57
but thereโ€™s a problem.
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ืื‘ืœ ื™ืฉ ื‘ืขื™ื”.
00:59
Few are willing to admit they support the troll
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ืžืขื˜ื™ื ืžื•ื›ื ื™ื ืœื”ื•ื“ื•ืช ืฉื”ื ืชื•ืžื›ื™ื ื‘ื˜ืจื•ืœ
01:02
on account of his controversial life choices.
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ื‘ืฉืœ ื‘ื—ื™ืจื•ืช ื”ื—ื™ื™ื ื”ืฉื ื•ื™ื•ืช ื‘ืžื—ืœื•ืงืช ืฉืœื•.
01:06
If you were to ask a troll supporter who she'll vote for,
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ืื ื”ื™ื™ืชื ืฉื•ืืœื™ื ืชื•ืžื›ืช ื˜ืจื•ืœ ื‘ืžื™ ืชื‘ื—ืจ,
01:09
thereโ€™s a good chance that sheโ€™ll claim to support the treeman,
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ื™ืฉ ืกื™ื›ื•ื™ ื˜ื•ื‘ ืฉื”ื™ื ืชื˜ืขืŸ ืฉืชืชืžื•ืš ื‘ืื™ืฉ ื”ืขืฆื™ื,
01:13
skewing your results.
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ื•ืชืกื™ื˜ ืืช ื”ืชื•ืฆืื•ืช ืฉืœื›ื.
01:16
Youโ€™re about to begin your rounds when a stranger offers you some cryptic advice:
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ืืชื ืขื•ืžื“ื™ื ืœื”ืชื—ื™ืœ ื‘ืกื‘ื‘ ืฉืœื›ื ื›ืฉื–ืจ ืžืฆื™ืข ืœื›ื ืขืฆื” ืงืจื™ืคื˜ื™ืช:
01:21
โ€œHereโ€™s the question that will save your neck: what have you got in your pocket?โ€
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โ€œื”ื ื” ื”ืฉืืœื” ืฉืชืฆื™ืœ ืืช ืฆื•ื•ืืจื›ื: ืžื” ื™ืฉ ืœื›ื ื‘ื›ื™ืก?โ€
01:27
You reach into your pocket and pull out... a silver coin,
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ืืชื ืžื•ืฉื™ื˜ื™ื ืืช ื”ื™ื“ ืœื›ื™ืก ื•ืžื•ืฆื™ืื™ื... ืžื˜ื‘ืข ื›ืกืฃ,
01:31
which has the current kingโ€™s head on one side and his tail on the other.
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ืฉื™ืฉ ืขืœื™ื• ืืช ืจืืฉ ื”ืžืœืš ื”ื ื•ื›ื—ื™ ื‘ืฆื“ ืื—ื“ ื•ื–ื ื‘ื• ืขืœ ื”ืื—ืจ.
01:37
How can you use it to conduct an accurate poll?
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ืื™ืš ืชื•ื›ืœื• ืœื”ืฉืชืžืฉ ื‘ื• ื›ื“ื™ ืœืขืจื•ืš ืกืงืจ ืžื“ื•ื™ื™ืง?
01:40
Pause here to figure it out yourself. Answer in 3
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ืขื™ืฆืจื• ืคื” ื›ื“ื™ ืœื”ื‘ื™ืŸ ื‘ืขืฆืžื›ื.
01:43
Answer in 2
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ืชืฉื•ื‘ื” ืขื•ื“ 2
01:46
Answer in 1
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ืชืฉื•ื‘ื” ืขื•ื“ 1
01:48
The trick here is to use the coin to add random chance
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ื”ื˜ืจื™ืง ืคื” ื”ื•ื ืœื”ืฉืชืžืฉ ื‘ืžื˜ื‘ืข ื›ื“ื™ ืœื”ื•ืกื™ืฃ ื”ืกืชื‘ืจื•ืช ืืงืจืื™ืช
01:52
to your interaction that will give troll supporters deniability.
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ืœืื™ื ื˜ืจืงืฆื™ื” ืฉืœื›ื ืฉืชืชืŸ ืืช ื™ื›ื•ืœืช ื”ื”ื›ื—ืฉื” ืœืชื•ืžื›ื™ ื”ื˜ืจื•ืœ.
01:57
In other words, youโ€™re looking for a system where when someone says โ€œtroll,โ€
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ื‘ืžื™ืœื™ื ืื—ืจื•ืช, ืืชื ืžื—ืคืฉื™ื ืžืขืจื›ืช ื‘ื” ื›ืฉืžื™ืฉื”ื• ืื•ืžืจ โ€œื˜ืจื•ืœ,โ€
02:01
it could either be because the coin somehow told them to,
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ื–ื” ื™ื›ื•ืœ ืœื”ื™ื•ืช ืื• ื‘ื’ืœืœ ืฉื”ืžื˜ื‘ืข ืืžืจ ืœื”ื ืœื”ื’ื™ื“,
02:05
or because they actually support the trollโ€”
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ืื• ื‘ื’ืœืœ ืฉื”ื ืœืžืขืฉื” ืชื•ืžื›ื™ื ื‘ื˜ืจื•ืœ --
02:08
and youโ€™d have no way to tell the difference.
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ื•ืœื ืชื”ื™ื” ืœื›ื ื“ืจืš ืœื”ื‘ื“ื™ืœ.
02:12
Youโ€™ll also need to know how frequently the coin skewed the results,
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ืืชื ื’ื ืชืฆื˜ืจื›ื• ืœื“ืขืช ื‘ืื™ื–ื” ืชื“ื™ืจื•ืช ื”ืžื˜ื‘ืข ืžืกื™ื˜ ืืช ื”ืชื•ืฆืื•ืช,
02:16
so you can account for it in your calculations.
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ื›ืš ืฉืชื•ื›ืœื• ืœืชืงืŸ ืืช ื–ื” ื‘ื—ื™ืฉื•ื‘ื™ื.
02:20
One solution is to have every pollee go into their house and flip the coin.
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ืคื™ืชืจื•ืŸ ืื—ื“ ื”ื•ื ืฉื›ืœ ื ืกืงืจ ื™ื›ื ืก ืœื‘ื™ืช ื•ื™ื˜ื™ืœ ืืช ื”ืžื˜ื‘ืข.
02:27
If it lands heads, they should tell you โ€œtroll,โ€
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ืื ื”ื•ื ื™ืจืื” ืจืืฉ, ื”ื ืฆืจื™ื›ื™ื ืœื”ื’ื™ื“ ืœื›ื โ€œื˜ืจื•ืœ,โ€
02:30
whether or not they actually support him.
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ื‘ื™ืŸ ืื ื”ื ืชื•ืžื›ื™ื ื‘ื• ืื• ืœื.
02:32
If it lands tails, they should tell you their actual preference.
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ืื ื™ืฆื ื–ื ื‘, ื”ื ืฆืจื™ื›ื™ื ืœื”ื’ื™ื“ ืืช ื”ื”ืขื“ืคื” ื”ืืžื™ืชื™ืช ืฉืœื”ื.
02:37
Hereโ€™s what happens:
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ื•ื”ื ื” ืžื” ืฉืงื•ืจื”:
02:39
you poll 200 voters, and 130 say theyโ€™ll vote for the troll.
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ืืชื ืกื•ืงืจื™ื 200 ื‘ื•ื—ืจื™ื, ื• 130 ืื•ืžืจื™ื ืฉื”ื ื™ืชืžื›ื• ื‘ื˜ืจื•ืœ.
02:44
For about 50%, or 100 of them, the coin will have landed heads.
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ืขื‘ื•ืจ ื‘ืขืจืš 50%, ืื• 100 ืžื”ื, ื”ืžื˜ื‘ืข ื™ื ื—ืช ืขืœ ืจืืฉ.
02:49
So you can subtract 100 troll votes off his total,
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ืื– ืืชื ื™ื›ื•ืœื™ื ืœื”ืคื—ื™ืช 100 ื‘ื—ื™ืจื•ืช ื‘ื˜ืจื•ืœ ืžื”ืกื›ื•ื ื”ื›ื•ืœืœ,
02:53
and know the trollโ€™s real support is 30 to 70, and heโ€™s very likely to lose.
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ื•ืœื“ืขืช ืฉื”ืชืžื™ื›ื” ื”ืืžื™ืชื™ืช ื‘ื˜ืจื•ืœ ื”ื™ื 30 ืขื“ 70, ื•ื™ืฉ ืกื™ื›ื•ื™ ื’ื‘ื•ื” ืฉื™ืคืกื™ื“.
03:00
The election comes around, but before the results can be certified
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ื”ื‘ื—ื™ืจื•ืช ืžื’ื™ืขื•ืช, ืื‘ืœ ืœืคื ื™ ืฉื”ืชื•ืฆืื•ืช ืžืื•ืฉืจื•ืช
03:04
a third party candidate swoops in and burns the treefellow to a crisp.
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ืžื•ืขืžื“ ืฉืœื™ืฉื™ ื ื›ื ืก ื•ืฉื•ืจืฃ ืืช ืžื•ืขืžื“ ื”ืขืฅ ืœืืคืจ.
03:10
The freshly signed and deeply flawed constitution mandates that this challenger
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ื”ื—ื•ืงื” ื”ื—ื“ืฉื” ื•ื”ืคื’ื•ืžื” ืื•ืžืจืช ืฉื”ืžื•ืขืžื“
03:15
gets to take his victimโ€™s place in a new election.
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ืžืงื‘ืœ ืืช ืžืงื•ื ื”ืงื•ืจื‘ืŸ ืฉืœื• ื‘ื‘ื—ื™ืจื•ืช ื—ื“ืฉื•ืช.
03:19
The Dormor Polling Agency sends you back out on the streets with your trusty coin.
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ืกื•ื›ื ื•ืช ื”ืกืงืจื™ื ื“ื•ืจืžื•ืจ ืฉื•ืœื—ืช ืืชื›ื ื—ื–ืจื” ืœืจื—ื•ื‘ื•ืช ืขื ื”ืžื˜ื‘ืข ื”ืืžื™ืŸ.
03:24
Only this time no one is comfortable admitting their preference:
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ืจืง ืฉื”ืคืขื ืืฃ ืื—ื“ ืœื ืžืจื’ื™ืฉ ื‘ื ื•ื— ืœื”ื•ื“ื•ืช ื‘ื”ืขื“ืคื” ืฉืœื”ื:
03:29
supporting the troll is still shameful,
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ืชืžื™ื›ื” ื‘ื˜ืจื•ืœ ื”ื™ื ืžื‘ื™ืฉื”,
03:31
and nobody wants to express support of a dragon who murdered his way into the race.
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ื•ืืฃ ืื—ื“ ืœื ืจื•ืฆื” ืœื”ื‘ื™ืข ืชืžื™ื›ื” ื‘ื“ืจืงื•ืŸ ืฉืจืฆื— ืืช ื“ืจื›ื• ืœืžืจื•ืฅ.
03:38
But your job is your job. How do you conduct an accurate poll now?
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ืื‘ืœ ื”ืขื‘ื•ื“ื” ืฉืœื›ื ื”ื™ื ื”ืขื‘ื•ื“ื” ืฉืœื›ื. ืื™ืš ืืชื ืขื•ืจื›ื™ื ืกืงืจ ืžื“ื•ื™ื™ืง ืขื›ืฉื™ื•?
03:42
Pause here to figure it out for yourself. Answer in 3
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ืขื™ืฆืจื• ืคื” ื›ื“ื™ ืœื”ื‘ื™ืŸ ื‘ืขืฆืžื›ื.
03:45
Answer in 2
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ืชืฉื•ื‘ื” ืขื•ื“ 2
03:48
Answer in 1
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ืชืฉื•ื‘ื” ืขื•ื“ 1
03:52
This time, instead of masking just one candidate preference,
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ื”ืคืขื, ื‘ืžืงื•ื ืœืžืกืš ืจืง ื”ืขื“ืคื” ืœืžื•ืขืžื“ ืื—ื“,
03:56
you need some way to disguise both.
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ืืชื ืฆืจื™ื›ื™ื ื“ืจืš ืœืžืกืš ืืช ืฉืชื™ื”ืŸ.
03:58
At the same time, you also need to leave space for some portion of the people
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ื‘ืื•ืชื• ื–ืžืŸ, ืืชื ื’ื ืฆืจื™ื›ื™ื ืœื”ืฉืื™ืจ ืžืงื•ื ืœื›ืžื•ืช ืžืกื•ื™ื™ืžืช ืฉืœ ืื ืฉื™ื
04:03
polled to express their true preference.
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ืฉื ืกืงืจื• ื›ื“ื™ ืœื”ื‘ื™ืข ืืช ื“ืขืชื ื”ืืžื™ืชื™ืช.
04:06
But a coin toss only has two possible outcomes... right?
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ืื‘ืœ ืœื”ื˜ืœืช ืžื˜ื‘ืข ื™ืฉ ืจืง ืฉืชื™ ืืคืฉืจื•ื™ื•ืช... ื ื›ื•ืŸ?
04:12
Suppose you have everyone flip the coin twiceโ€”
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ื ื ื™ื— ืฉืืชื ืžื‘ืงืฉื™ื ืžื›ื•ืœื ืœื”ื˜ื™ืœ ืืช ื”ืžื˜ื‘ืข ืคืขืžื™ื™ื --
04:16
now there are four possible results.
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ืขื›ืฉื™ื• ื™ืฉ ืืจื‘ืข ืชื•ืฆืื•ืช ืืคืฉืจื™ื•ืช.
04:19
You can tell the people who flip heads twice in a row
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ืืชื ื™ื›ื•ืœื™ื ืœื”ื’ื™ื“ ืœืื ืฉื™ื ืฉื”ื˜ื™ืœื• ืจืืฉ ืคืขืžื™ื™ื ื‘ืจืฆืฃ
04:23
to report support for the troll;
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ืœื“ื•ื•ื— ืฉื”ื ืชื•ืžื›ื™ื ื‘ื˜ืจื•ืœ;
04:25
those who get tails twice in a row to report dragon;
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ืืœื” ืฉืžืงื‘ืœื™ื ืคืขืžื™ื™ื ื–ื ื‘ ื‘ืจืฆืฃ ืœื“ื•ื•ื— ื“ืจืงื•ืŸ;
04:29
and those with any other combination to declare their true preference.
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ื•ืืœื” ืขื ืฆืจื•ืคื™ื ืฉื•ื ื™ื ืœื“ื•ื•ื— ืืช ื”ื”ืขื“ืคื” ื”ืืžื™ืชื™ืช ืฉืœื”ื.
04:35
The chances of getting either two heads or two tails in a row
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ื”ืกื™ื›ื•ื™ื™ื ืœืงื‘ืœ ืื• ืฉื ื™ ืจืืฉื™ื ืื• ืฉื ื™ ื–ื ื‘ื•ืช ื‘ืจืฆืฃ
04:39
are 50% times 50%โ€” or 25%.
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ื”ื 50% ื›ืคื•ืœ 50% -- ืื• 25%.
04:44
Subtracting that proportion of the total respondents
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ื”ืคื—ืชืช ื”ื™ื—ืก ื”ื–ื” ืžืกืš ื”ืžื’ื™ื‘ื™ื
04:47
from each candidateโ€™s score should give you something close
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ืžืชื•ืฆืื” ืฉืœ ื›ืœ ืžื•ืขืžื“ ืฆืจื™ื›ื” ืœืชืช ืœื›ื ืžืฉื”ื• ืงืจื•ื‘
04:51
to the real distribution.
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ืœื”ืชืคื–ืจื•ืช ื”ืืžื™ืชื™ืช.
04:53
This time, 105 respondents announced themselves in favor of the troll
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ื”ืคืขื, 105 ืžื’ื™ื‘ื™ื ืžื›ืจื™ื–ื™ื ืขืœ ืขืฆืžื ื›ืชื•ืžื›ื™ื ื‘ื˜ืจื•ืœ
04:59
and 95 for the dragon.
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ื• 95 ื›ืชื•ืžื›ื™ื ื‘ื“ืจืงื•ืŸ.
05:01
Out of the total, the coin will make 25%
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ืžืชื•ืš ื”ืกืš ื”ื›ื•ืœืœ, ื”ืžื˜ื‘ืข ื™ื”ื•ื•ื” 25%
05:04
or 50 respond troll and another 50 respond dragon.
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ืื• 50 ืžื’ื™ื‘ื™ื ืœื˜ืจื•ืœ ื•50 ื ื•ืกืคื™ื ืœื“ืจืงื•ืŸ.
05:10
Subtracting 50 from each result reveals that voters seem to prefer the troll
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ืื ืžืคื—ื™ืชื™ื 50 ืžื›ืœ ืชื•ืฆืื” ืžื’ืœื™ื ืฉื”ื‘ื•ื—ืจื™ื ืžืขื“ื™ืคื™ื ืืช ื”ื˜ืจื•ืœ
05:15
by a margin of about 55 to 45.
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ื‘ื”ืคืจืฉ ืฉืœ ื‘ืขืจืš 55 ืœ 45.
05:19
Itโ€™s close, but as predicted, the troll wins the election,
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ื–ื” ืงืจื•ื‘, ืื‘ืœ ื›ืžื• ืฉื ืฆืคื”, ื”ื˜ืจื•ืœ ื–ื•ื›ื” ื‘ื‘ื—ื™ืจื•ืช,
05:23
and you live to poll another day.
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ื•ืืชื ื—ื™ื™ื ืœื”ืขื‘ื™ืจ ืขื•ื“ ืกืงืจ.
ืขืœ ืืชืจ ื–ื”

ืืชืจ ื–ื” ื™ืฆื™ื’ ื‘ืคื ื™ื›ื ืกืจื˜ื•ื ื™ YouTube ื”ืžื•ืขื™ืœื™ื ืœืœื™ืžื•ื“ ืื ื’ืœื™ืช. ืชื•ื›ืœื• ืœืจืื•ืช ืฉื™ืขื•ืจื™ ืื ื’ืœื™ืช ื”ืžื•ืขื‘ืจื™ื ืขืœ ื™ื“ื™ ืžื•ืจื™ื ืžื”ืฉื•ืจื” ื”ืจืืฉื•ื ื” ืžืจื—ื‘ื™ ื”ืขื•ืœื. ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ื”ืžื•ืฆื’ื•ืช ื‘ื›ืœ ื“ืฃ ื•ื™ื“ืื• ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ ืžืฉื. ื”ื›ืชื•ื‘ื™ื•ืช ื’ื•ืœืœื•ืช ื‘ืกื ื›ืจื•ืŸ ืขื ื”ืคืขืœืช ื”ื•ื•ื™ื“ืื•. ืื ื™ืฉ ืœืš ื”ืขืจื•ืช ืื• ื‘ืงืฉื•ืช, ืื ื ืฆื•ืจ ืื™ืชื ื• ืงืฉืจ ื‘ืืžืฆืขื•ืช ื˜ื•ืคืก ื™ืฆื™ืจืช ืงืฉืจ ื–ื”.

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