Can you solve the riddle and escape Hades? - Dan Finkel

2,909,829 views ใƒป 2020-10-13

TED-Ed


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

ืชืจื’ื•ื: Ido Dekkers ืขืจื™ื›ื”: Alsa Saal
00:07
Maybe the fates got clumsy.
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ืื•ืœื™ ื”ืžื–ืœ ื ืขืฉื” ืžืจื•ืฉืœ.
00:09
Maybe Poseidon had one of his angry days.
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ืื•ืœื™ ืœืคื•ืกื™ื“ื•ืŸ ื”ื™ื” ืื—ื“ ืžื”ื™ืžื™ื ื”ื’ืจื•ืขื™ื ืฉืœื•.
00:12
However it happened, the underworld is overcrowded,
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ืื™ืš ืฉื–ื” ืœื ืงืจื”, ื”ืขื•ืœื ื”ืชื—ืชื•ืŸ ืขืžื•ืก,
00:15
and Zeus has ordered Hades to let some spirits out.
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ื•ื–ืื•ืก ืฆื™ื•ื•ื” ืขืœ ื”ืื“ืก ืœืฉื—ืจืจ ื›ืžื” ื ืฉืžื•ืช.
00:20
Hades arranges all the souls of the dead in a line before Cerberus.
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ื”ืื“ืก ืื™ืจื’ืŸ ืืช ื›ืœ ื”ื ืฉืžื•ืช ืฉืœ ื”ืžืชื™ื ื‘ื˜ื•ืจ ืžื•ืœ ืกืจื‘ืจื•ืก.
00:24
When one of his three heads bites down on the soul in front of it,
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ื›ืฉืื—ื“ ืžืฉืœื•ืฉืช ืจืืฉื™ื• ื™ื ืฉื•ืš ืืช ื”ื ืฉืžื” ืžื•ืœื•,
00:28
theyโ€™ll get returned to the land of the living.
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ื”ื ื™ื—ื–ืจื• ืœืขื•ืœื ื”ื—ื™ื™ื.
00:31
Anyone to the left must get out of line and stay in Hades forever.
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ื›ืœ ืžื™ ืฉื ืžืฆื ืžืฉืžืืœ ื—ื™ื™ื‘ ืœืฆืืช ืžื”ืชื•ืจ ื•ืœื”ืฉืืจ ืขื ื”ืื“ืก ืœืชืžื™ื“.
00:36
And everyone else shuffles forward, at which point Cerberus will feed again.
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ื•ื›ืœ ื”ืื—ืจื™ื ื™ื™ื“ื—ืคื• ืงื“ื™ืžื”, ื•ืื– ืกืจื‘ืจื•ืก ื™ืื›ืœ ืฉื•ื‘.
00:41
Each of the dogโ€™s heads has an equal chance of being the one to bite each time,
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ืœื›ืœ ืื—ื“ ืžืจืืฉื™ ื”ื›ืœื‘ื™ื ื™ืฉ ืกื™ื›ื•ื™ ืฉื•ื•ื” ืœื”ื™ื•ืช ื–ื” ืฉื ื•ืฉืš ื‘ื›ืœ ืคืขื,
00:47
and no two ever bite simultaneously.
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ื•ืืฃ ืคืขื ื”ื ืœื ื ื•ืฉื›ื™ื ื™ื—ื“.
00:51
Unfortunately, Hadesโ€™ minions forgot to tell you what was happening,
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ืœืžืจื‘ื” ื”ืฆืขืจ, ื”ืžื™ื ื™ื•ื ื™ื ืฉืœ ื”ืื“ืก ืฉื›ื—ื• ืœื”ื’ื™ื“ ืœื›ื ืžื” ืงื•ืจื”,
00:55
and by the time you show up there are only 99 souls left in line.
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ื•ืขื“ ืฉืืชื ืžื’ื™ืขื™ื ื ืฉืืจื• ืจืง 99 ื ืฉืžื•ืช ื‘ืชื•ืจ.
01:00
Hades looks furious and drawing attention to yourself wonโ€™t end well.
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ื”ืื“ืก ื ืจืื” ื–ื•ืขื ื•ืžืฉื™ื›ืช ืชืฉื•ืžืช ืœื‘ ืืœื™ื›ื ืœื ืชื™ื’ืžืจ ื˜ื•ื‘.
01:04
But suddenly, time freezes, and Hermes steps out of the shadows.
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ืื‘ืœ ืคืชืื•ื, ื”ื–ืžืŸ ืงื•ืคื, ื•ื”ืจืžืก ื™ื•ืฆื ืžื”ืฆืœืœื™ื.
01:09
He tells you he can instantly put you into the line,
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ื”ื•ื ืื•ืžืจ ืœื›ื ืฉื”ื•ื ื™ื›ื•ืœ ืœื”ื›ื ื™ืก ืืชื›ื ืžื™ื™ื“ื™ืช ืœืชื•ืจ,
01:12
and no one will realize what happened.
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ื•ืืฃ ืื—ื“ ืœื ื™ื“ืข ืžื” ืงืจื”.
01:15
But heโ€™ll only grant his grace to someone clever enough
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ืื‘ืœ ื”ื•ื ื™ืขื ื™ืง ืืช ื”ื—ืกื“ ื”ื–ื” ืจืง ืœืžื™ ืฉื—ื›ื ืžืกืคื™ืง
01:19
to take full advantage of it.
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ืœื ืฆืœ ืืช ื”ืžืฆื‘.
01:21
Choose the best place in line and heโ€™ll give you the spot.
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ื‘ื—ืจื• ืืช ื”ืžืงื•ื ื”ื˜ื•ื‘ ื‘ื™ื•ืชืจ ื‘ืชื•ืจ ื•ื”ื•ื ื™ืชืŸ ืœื›ื ืืช ื”ืžืงื•ื.
01:24
Choose wrong, and heโ€™ll leave you to rot.
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ื‘ื—ืจื• ืœื ื ื›ื•ืŸ, ื•ื”ื•ื ื™ืฉืื™ืจ ืืชื›ื ืœื”ืจืงื‘.
01:27
Which spot should you pick?
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ืื™ื–ื” ืžื™ืงื•ื ืชื‘ื—ืจื•?
01:29
Pause the video to figure it out yourself.
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ืขืฆืจื• ืคื” ืืช ื”ืกืจื˜ื•ืŸ ื›ื“ื™ ืœื”ื‘ื™ืŸ ื‘ืขืฆืžื›ื.
01:31
Answer in 3
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ืชืฉื•ื‘ื” ื‘ืขื•ื“ 3
01:32
Answer in 2
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ืชืฉื•ื‘ื” ื‘ืขื•ื“ 2
01:35
Answer in 1
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ืชืฉื•ื‘ื” ื‘ืขื•ื“ 1
01:37
Itโ€™s possible to calculate the exact probability of going free
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ื–ื” ืืคืฉืจื™ ืœื—ืฉื‘ ืืช ื”ื”ืกืชื‘ืจืช ื”ืžื“ื•ื™ื™ืงืช ืฉืœ ื™ืฆื™ืื” ืœื—ื•ืคืฉื™
01:41
in all 100 spots.
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ื‘ื›ืœ 100 ื”ืžืงื•ืžื•ืช.
01:43
But thereโ€™s a much simpler path to the solution
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ืื‘ืœ ื™ืฉ ื“ืจืš ื”ืจื‘ื” ื™ื•ืชืจ ืคืฉื•ื˜ื” ืœืคืชืจื•ืŸ
01:46
that requires surprisingly little calculation.
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ืฉื“ื•ืจืฉืช ืžืขื˜ ืžืื•ื“ ื—ื™ืฉื•ื‘, ื‘ืื•ืคืŸ ืžืคืชื™ืข.
01:49
Imagine being anywhere in line.
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ื“ืžื™ื™ื ื• ืฉื”ื™ื™ืชื ื‘ื›ืœ ืžืงื•ื ื‘ืชื•ืจ.
01:52
Way up at the front, one of the three heads will pick someone at random,
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ืžืžืฉ ืœืคื ื™ื, ืื—ื“ ืžืฉืœื•ืฉืช ื”ืจืืฉื™ื ื™ื‘ื—ืจ ืžื™ืฉื”ื• ื‘ืื•ืคืŸ ืืงืจืื™,
01:56
and youโ€™ll move forward 1, 2, or 3 spaces.
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ื•ืืชื ืชืขื‘ืจื• ืงื“ื™ืžื” 1,2 ืื• 3 ืžืงื•ืžื•ืช.
01:59
Since each is equally likely,
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ืžืื—ืจ ืฉื›ืœ ืื—ื“ ืืคืฉืจื™ ื‘ืื•ืคืŸ ืฉื•ื•ื”,
02:02
your chance of survival from wherever you started
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ื”ืกื™ื›ื•ื™ื™ื ืฉืœื›ื ืœื”ืฆืœื” ืžื›ืœ ืžืงื•ื ืžืžื ื• ื”ืชื—ืœืชื
02:05
is the average of the chances from each of the three spaces in front of you.
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ื”ื•ื ื”ืžืžื•ืฆืข ืฉืœ ื”ืกื™ื›ื•ื™ื™ื ืžื›ืœ ืื—ื“ ืžืฉืœื•ืฉืช ื”ืžืงื•ืžื•ืช ื”ืืœื” ืฉืœืคื ื™ื›ื.
02:10
And this is where you can find a huge shortcut.
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ื•ืคื” ืืชื ื™ื›ื•ืœื™ื ืœืžืฆื•ื ืงื™ืฆื•ืจ ื“ืจืš ืื“ื™ืจ.
02:15
Averages must be on or between the extremes of what youโ€™re averagingโ€”
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ืžืžื•ืฆืขื™ื ื—ื™ื™ื‘ื™ื ืœื”ื™ื•ืช ืขืœ ืื• ื‘ื™ืŸ ืฉื ื™ ื”ืงื™ืฆื•ื ื™ื ืฉืœ ืžื” ืฉืืชื ืžืžืฆืขื™ื --
02:20
they can never be higher than the highest value
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ื”ื ืœืขื•ืœื ืœื ื™ื›ื•ืœื™ื ืœื”ื™ื•ืช ื’ื‘ื•ื”ื™ื ื™ื•ืชืจ ืžื”ืขืจืš ื”ื›ื™ ื’ื‘ื•ื”
02:23
or lower than the lowest.
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ืื• ื ืžื•ื›ื™ื ืžื”ื ืžื•ืš ื‘ื™ื•ืชืจ.
02:25
So whatever your chances of survival are where you start,
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ืœื ืžืฉื ื” ืžื” ืกื™ื›ื•ื™ื™ ื”ื”ืฉืจื“ื•ืช ืฉืœื›ื ื‘ืžืงื•ื ื‘ื• ืชืชื—ื™ืœื•,
02:29
one of the three places in front of you is at least as good,
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ืื—ื“ ืžืฉืœื•ืฉืช ื”ืžืงื•ืžื•ืช ืœืคื ื™ื›ื ื”ื ื˜ื•ื‘ื™ื ืœืคื—ื•ืช ื‘ืื•ืชื” ืžื™ื“ื”,
02:33
and probably better.
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ื•ื›ื ืจืื” ื˜ื•ื‘ื™ื ื™ื•ืชืจ.
02:35
This observation is incredibly powerful.
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ื”ืื‘ื—ื ื” ื”ื–ื• ืžื•ืขื™ืœื” ืžืื•ื“.
02:38
It means that wherever you are in line,
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ื–ื” ืื•ืžืจ ืฉืœื ืžืฉื ื” ืื™ืคื” ืืชื ื‘ืชื•ืจ,
02:41
itโ€™d be wise to trade your place for one of the three spots in front of you.
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ื–ื” ื™ื”ื™ื” ื—ื›ื ืœื”ื—ืœื™ืฃ ืืช ื”ืžืงื•ื ืฉืœื›ื ืœืื—ื“ ืžืฉืœื•ืฉืช ื”ืžืงื•ืžื•ืช ืœืคื ื™ื›ื.
02:46
Letโ€™s ignore which for now and think of them as a trioโ€”
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ื‘ื•ืื• ื ืชืขืœื ืžืื™ื–ื” ื›ืจื’ืข ื•ื ื—ืฉื•ื‘ ืขืœื™ื”ื ื›ืฉืœื™ืฉื™ื” --
02:50
this trioโ€™s maximum value is better than this trioโ€™s, and so on.
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ื”ืขืจืš ื”ืžืงืกื™ืžืœื™ ืฉืœ ื”ืฉืœื™ืฉื™ื” ื”ื–ื• ื˜ื•ื‘ ื™ื•ืชืจ ืžื”ืฉืœื™ืฉื™ื” ื”ื–ื•, ื•ื›ืš ื”ืœืื”.
02:54
Keep going and youโ€™ll reach the front...
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ื”ืžืฉื™ื›ื• ื•ืชื’ื™ืขื• ืœื—ื–ื™ืช...
02:57
These three spots must contain the extreme valuesโ€”
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ืฉืœื•ืฉืช ื”ืžืงื•ืžื•ืช ื”ืืœื• ื—ื™ื™ื‘ื™ื ืœื”ื›ื™ืœ ืืช ื”ืขืจื›ื™ื ื”ืงื™ืฆื•ื ื™ื™ื --
03:01
the best and worst probabilitiesโ€”
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ื”ื”ืกืชื‘ืจื•ื™ื•ืช ื”ื˜ื•ื‘ื” ื•ื”ื’ืจื•ืขื” ื‘ื™ื•ืชืจ --
03:04
for the entire line.
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ื‘ื›ืœ ื”ืชื•ืจ.
03:05
In other words, theyโ€™re all we need to consider.
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ื‘ืžื™ืœื™ื ืื—ืจื•ืช, ื”ื ื›ืœ ืžื” ืฉืื ื—ื ื• ืฆืจื™ื›ื™ื ืœืฉืงื•ืœ.
03:09
Place 1 is bad.
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ืžืงื•ื ืžืกืคืจ 1 ื’ืจื•ืข.
03:11
Head one would save you, and the other two doom you forever.
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ื”ืจืืฉ ื”ืจืืฉื•ืŸ ื™ืฆื™ืœ ืืชื›ื, ื•ื”ืื—ืจื™ื ื™ื“ื•ื ื• ืืชื›ื ืœื ืฆื—.
03:14
Thatโ€™s just a 1 in 3 chance to escape.
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ื–ื” ืจืง ื”ื–ื“ืžื ื•ืช ืฉืœ 1 ืž 3 ืœื‘ืจื•ื—.
03:17
Place 2 is better: head two is great,
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ืžืงื•ื 2 ื˜ื•ื‘ ื™ื•ืชืจ: ื”ืจืืฉ ื”ืฉื ื™ ืžืขื•ืœื”,
03:21
head 3 is bad, and head 1 is ok in that it gives you another chance.
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ื”ืจืืฉ ื”ืฉืœื™ืฉื™ ื’ืจื•ืข, ื•ื”ืจืืฉ ื”ืจืืฉื•ืŸ ื‘ืกื“ืจ ื‘ื–ื” ืฉื”ื•ื ื ื•ืชืŸ ืœื›ื ื”ื–ื“ืžื ื•ืช ื ื•ืกืคืช.
03:26
But place 3 is best, because head 3 saves you
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ืื‘ืœ ืžืงื•ื 3 ื”ื•ื ื”ื›ื™ ื˜ื•ื‘, ื‘ื’ืœืœ ืฉืจืืฉ 3 ืžืฆื™ืœ ืืชื›ื
03:31
while heads 1 and 2 both give you extra chances.
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ื‘ืขื•ื“ ืจืืฉื™ื 1 ื• 2 ื ื•ืชื ื™ื ืœื›ื ื”ื–ื“ืžื ื•ื™ื•ืช ื ื•ืกืคื•ืช.
03:35
If you did want to consider the exact probabilities,
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ืื ื”ื™ื™ืชื ืจื•ืฆื™ื ืœืฉืงื•ืœ ืืช ื”ื”ืกืชื‘ืจื•ื™ื•ืช ื”ืžื“ื•ื™ื™ืงื•ืช,
03:39
the odds of surviving in place 3 are 16 out of 27, or close to 60%.
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ื”ืกื™ื›ื•ื™ื™ื ืœืฉืจื•ื“ ื‘ืžืงื•ื 3 ื”ื•ื ื‘ืขืจืš 16 ืžืชื•ืš 27, ืื• ืงืจื•ื‘ ืœ 60%.
03:45
The spots later in line tend to be very close to having a 50% chance of survival.
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ื”ืžืงื•ืžื•ืช ื‘ื”ืžืฉืš ื”ืชื•ืจ ื ื•ื˜ื™ื ืœื”ื™ื•ืช ืงืจื•ื‘ื™ื ืžืื•ื“ ืœ 50% ืกื™ื›ื•ื™ ืœืฉืจื•ื“.
03:51
Why 50%?
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ืœืžื” 50%?
03:52
Because every time Cerberus sends one soul up to be reborn,
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ื‘ื’ืœืœ ืฉื‘ื›ืœ ืคืขื ืฉืกืจื‘ืจื•ืก ืฉื•ืœื— ื ืฉืžื” ืœื”ื•ื•ืœื“ ืžื—ื“ืฉ,
03:57
he leaves 0, 1, or 2 souls in the underworld.
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ื”ื•ื ืžืฉืื™ืจ 0,1 ืื• 2 ื ืฉืžื•ืช ื‘ืขื•ืœื ื”ืชื—ืชื•ืŸ.
04:01
That averages out to one person staying for each one who gets freed.
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ื–ื” ืžืชืžืฆืข ืœืื“ื ืื—ื“ ืฉื ืฉืืจ ืขื‘ื•ืจ ื›ืœ ืื“ื ืฉืžืฉื•ื—ืจืจ.
04:07
But you can beat those odds handily with what you now know.
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ืื‘ืœ ืืชื ื™ื›ื•ืœื™ื ืœื ืฆื— ืืช ื”ืกื™ื›ื•ื™ื™ื ื‘ืงืœื•ืช ืขื ืžื” ืฉืืชื ื™ื•ื“ืขื™ื.
04:11
Hermes has places to be, and so do you.
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ืœื”ืจืžืก ื™ืฉ ืžืงื•ืžื•ืช ืœื”ื™ื•ืช ื‘ื”ื, ื•ื’ื ืœื›ื.
04:14
He rewards your insight by sneaking you into the third spot.
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ื”ื•ื ื’ื•ืžืœ ืœื›ื ืขืœ ื”ืชื•ื‘ื ื” ื‘ื›ืš ืฉื”ื•ื ืžื’ื ื™ื‘ ืืชื›ื ืœืžืงื•ื ื”ืฉืœื™ืฉื™.
04:18
And from there itโ€™ll be just a short wait to learn your ultimate fate.
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ื•ืžืฉื ื–ื• ืชื”ื™ื” ืจืง ื”ืžืชื ื” ืงืฆืจื” ืขื“ ืฉืชื“ืขื• ืืช ื”ื’ื•ืจืœ ื”ืกื•ืคื™ ืฉืœื›ื.
ื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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