Can you solve Dongle's Difficult Dilemma? - Dennis E. Shasha

2,155,328 views ใƒป 2021-04-26

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
According to legend, when this planet was young and molten,
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ืœืคื™ ื”ืื’ื“ื”, ื›ืฉื”ืคืœื ื˜ื” ื”ื™ืชื” ืฆืขื™ืจื” ื•ืžื•ืชื›ืช,
00:10
three galactic terraformers shaped it into a paradise.
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ืฉืœื•ืฉื” ืžืขืฆื‘ื™ ืขื•ืœืžื•ืช ื’ืœืงื˜ื™ื™ื ืขื™ืฆื‘ื• ืื•ืชื” ืœื’ืŸ ืขื“ืŸ.
00:15
When their work was done, they sought out new worlds,
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ื›ืฉืขื‘ื•ื“ืชื ื”ืกืชื™ื™ืžื”, ื”ื ื—ื™ืคืฉื• ืขื•ืœืžื•ืช ื—ื“ืฉื™ื,
00:18
but left the source of their power behind:
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ืื‘ืœ ื”ืฉืื™ืจื• ืžืื—ื•ืจ ืืช ื›ื•ื—ื:
00:21
three powerful golden hexagons,
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ืฉืœื•ืฉื” ืžืฉื•ืฉื™ื ืžื•ื–ื”ื‘ื™ื,
00:25
hidden within dungeons full of traps and monsters.
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ื—ื‘ื•ื™ื™ื ื‘ืžืจืชืคื™ื ืžืœืื™ื ื‘ืžืœื›ื•ื“ื•ืช ื•ืžืคืœืฆื•ืช.
00:28
If one person were to bring all three hexagons together,
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ืื ืื“ื ืื—ื“ ื™ื•ื›ืœ ืœืื—ื“ ืืช ื›ืœ ืฉืœื•ืฉืช ื”ืžืฉื•ืฉื™ื,
00:32
they could reinvent the world however they saw fit.
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ื”ื ื™ื•ื›ืœื• ืœื”ืžืฆื™ื ืžื—ื“ืฉ ืืช ื”ืขื•ืœื ื›ืจืฆื•ื ื.
00:36
That was thousands of years ago.
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ื–ื” ื”ื™ื” ืœืคื ื™ ืืœืคื™ ืฉื ื™ื.
00:39
Today, youโ€™ve learned of Gordon, an evil wizard dead set on collecting the hexagons
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ื”ื™ื•ื, ื’ื™ืœื™ืชื ืฉื’ื•ืจื“ื•ืŸ, ืžื›ืฉืฃ ืžืจื•ืฉืข ื™ืฆื ืœืืกื•ืฃ ืืช ื”ืžืฉื•ืฉื™ื
00:45
and enslaving the world to his will.
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ื•ืœืฉืขื‘ื“ ืืช ื”ืขื•ืœื ื›ืจืฆื•ื ื•.
00:48
So you set off on a quest to get them first,
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ืื– ืืชื ื™ื•ืฆืื™ื ืœืžืกืข ืœื”ืฉื™ื’ ืื•ืชื ืงื•ื“ื,
00:52
adventuring through fire, ice, and sand.
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ื™ื•ืฆืื™ื ืœืชื•ืš ื”ืืฉ, ื”ืงืจื— ื•ื”ื—ื•ืœ.
00:56
Yet each time, you find that someone else got there first.
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ื•ืขื“ื™ื™ืŸ ื›ืœ ืคืขื, ืืชื ืžื’ืœื™ื ืฉืžื™ืฉื”ื• ืื—ืจ ื”ื’ื™ืข ืœืฉื ืงื•ื“ื.
01:00
Not Gordon, but a merchant named Dongle.
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ืœื ื’ื•ืจื“ื•ืŸ, ืืœื ืกื•ื—ืจ ื‘ืฉื ื“ื•ื ื’ืœ.
01:04
At the end of the third dungeon. you find a note inviting you to Dongleโ€™s castle.
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ื‘ืกื•ืฃ ื”ืžืจืชืฃ ื”ืฉืœื™ืฉื™. ืืชื ืžื’ืœื™ื ืคืชืง ืฉืžื–ืžื™ืŸ ืืชื›ื ืœื˜ื™ืจื” ืฉืœ ื“ื•ื ื’ืœ.
01:09
You show up with a wallet bursting with the 99 gems
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ืืชื ืžื•ืคื™ืขื™ื ืขื ืืจื ืง ืžืœื 99 ืื‘ื ื™ ื—ืŸ
01:13
youโ€™ve collected in your travels,
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ืฉืืกืคืชื ื‘ืžืกืขื•ืชื™ื›ื,
01:14
arriving just moments before Gordon, who also has 99 gems.
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ืžื’ื™ืขื™ื ืจืง ืจื’ืขื™ื ืœืคื ื™ ื’ื•ืจื“ื•ืŸ, ืฉื’ื ืœื• ื™ืฉ 99 ืื‘ื ื™ ื—ืŸ.
01:20
Dongle has not only collected the golden hexagons,
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ื“ื•ื ื’ืœ ืœื ืจืง ืืกืฃ ืืช ื”ืžืฉื•ืฉื™ื ื”ืžื•ื–ื”ื‘ื™ื,
01:24
but heโ€™s used them to create 5 silver hexagons,
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ืืœื ื”ืฉืชืžืฉ ื‘ื”ื ื›ื“ื™ ืœื™ืฆื•ืจ 5 ืžืฉื•ืฉื™ื ื›ืกื•ืคื™ื,
01:28
just as powerful as their golden counterparts.
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ื—ื–ืงื™ื ื›ืžื• ื“ื•ืžื™ื”ื ื”ืžื•ื–ื”ื‘ื™ื.
01:31
Why did Dongle do all this?
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ืœืžื” ื“ื•ื ื’ืœ ืขืฉื” ืืช ื›ืœ ื–ื”?
01:33
Because thereโ€™s one thing he loves above all else: auctions.
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ื‘ื’ืœืœ ืฉื™ืฉ ื“ื‘ืจ ืื—ื“ ืฉื”ื•ื ืื•ื”ื‘ ื™ื•ืชืจ ืžื”ื›ืœ: ืžื›ื™ืจื•ืช ืคื•ืžื‘ื™ื•ืช.
01:38
You and the evil wizard will compete to win the hexagons,
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ืืชื ื•ื”ืžื›ืฉืฃ ื”ืžืจื•ืฉืข ืชืชื—ืจื• ื›ื“ื™ ืœื–ื›ื•ืช ื‘ืžืฉื•ืฉื™ื,
01:43
starting with the three golden ones,
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ืžืชื—ื™ืœื™ื ื‘ืฉืœื•ืฉืช ื”ืžื•ื–ื”ื‘ื™ื,
01:45
making one bid for each item as it comes up.
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ื›ืฉืืชื ืžืฆื™ืขื™ื ืขืœ ื›ืœ ืื—ื“ ืžื”ื ื›ืฉื”ื•ื ืžื•ืคื™ืข.
01:49
The winners of ties will alternate, starting with you.
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ื”ื–ื•ื›ื™ื ื‘ืฉื•ื•ื™ื•ืŸ ื™ืชื—ืœืคื•, ื”ื—ืœ ื‘ื›ื.
01:53
Whoever first collects a trio of either golden or silver hexagons
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ืžื™ ืฉื™ืืกื•ืฃ ืฉืœื™ืฉื™ื” ืฉืœ ืžืฉื•ืฉื™ื ืžื•ื–ื”ื‘ื™ื ืื• ื›ืกื•ืคื™ื
01:58
can use their power to recreate the world.
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ื™ื•ื›ืœ ืœื”ืฉืชืžืฉ ื‘ื›ื•ื—ื• ื›ื“ื™ ืœื™ืฆื•ืจ ืžื—ื“ืฉ ืืช ื”ืขื•ืœื.
02:01
Youโ€™ve already bid 24 gems on the first,
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ื›ื‘ืจ ื”ืฆืขืชื 24 ืื‘ื ื™ ื—ืŸ ืขืœ ื”ืจืืฉื•ืŸ,
02:05
when you realize that your rival has a dastardly advantage:
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ื›ืฉืืชื ืžื‘ื™ื ื™ื ืฉืœื™ืจื™ื‘ ืฉืœื›ื ื™ืฉ ื™ืชืจื•ืŸ ืžืกื•ืจื‘ืœ:
02:09
a mirror that lets him see what youโ€™re bidding.
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ืžืจืื” ืฉืžืืคืฉืจืช ืœื• ืœืจืื•ืช ืžื” ืืชื ืžืฆื™ืขื™ื.
02:13
He bids zero, and you win the first hexagon outright.
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ื”ื•ื ืžืฆื™ืข ืืคืก, ื•ืืชื ื–ื•ื›ื™ื ื‘ืžืฉื•ืฉื” ื”ืจืืฉื•ืŸ.
02:17
Whatโ€™s your strategy to win a matching trio of hexagons before your rival?
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ืžื” ื”ืืกื˜ืจื˜ื’ื™ื” ืฉืœื›ื ืœื–ื›ื•ืช ื‘ืฉืœื™ืฉื™ื” ืžืชืื™ืžื” ืœืคื ื™ ื™ืจื™ื‘ื›ื?
02:22
Pause here to figure it out for yourself.
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ืขื™ืฆืจื• ืคื” ื›ื“ื™ ืœื”ื‘ื™ืŸ ื‘ืขืฆืžื›ื.
02:24
Answer in 3
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ืชืฉื•ื‘ื” ืขื•ื“ 3
02:25
Answer in 2
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ืชืฉื•ื‘ื” ืขื•ื“ 2
02:27
Answer in 1
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ืชืฉื•ื‘ื” ืขื•ื“ 1
02:31
Dongleโ€™s dangled a difficult dilemma.
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ื“ื•ื ื’ืœ ื™ืฆืจ ื“ื™ืœืžื” ืงืฉื”.
02:33
Do you spend big to try to win the golden hexagons outright?
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ื”ืื ืืชื ืžื‘ื–ื‘ื–ื™ื ื‘ื’ื“ื•ืœ ื•ืžื ืกื™ื ืœื–ื›ื•ืช ื‘ืžืฉื•ืฉื™ื ื”ืžื•ื–ื”ื‘ื™ื ืžื™ื™ื“?
02:37
Save as much as possible for silver? Or something in-between?
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ืœื—ืกื•ืš ื›ื›ืœ ื”ื™ื•ืชืจ ืœื›ืกื•ืคื™ื? ืื• ืžืฉื”ื• ื‘ื™ืŸ ืœื‘ื™ืŸ?
02:42
Gordon can use his magic mirror and 99 gems
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ื’ื•ืจื“ื•ืŸ ื™ื›ื•ืœ ืœื”ืฉืชืžืฉ ื‘ืžืจืืช ื”ืงืกืžื™ื ืฉืœื• ื• 99 ืื‘ื™ ื”ื—ืŸ
02:45
to make sure that no matter what you bid on the second gold,
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ื›ื“ื™ ืœื”ื‘ื˜ื™ื— ืฉืœื ืžืฉื ื” ืžื” ืชืฆื™ืขื• ืขืœ ื”ืžื•ื–ื”ื‘ ื”ืฉื ื™,
02:49
he can bid one more and block you.
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ื”ื•ื ื™ื•ื›ืœ ืœื”ืฆื™ืข ืื—ื“ ื™ื•ืชืจ ื›ื“ื™ ืœื—ืกื•ื ืืชื›ื.
02:51
So the real question isโ€” how can you force Gordon to spend enough on the golds
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ืื– ื”ืฉืืœื” ื”ืืžื™ืชื™ืช ื”ื™ื -- ืื™ืš ืืชื ื™ื›ื•ืœื™ื ืœื”ื›ืจื™ื— ืืช ื’ื•ืจื“ื•ืŸ ืœื‘ื–ื‘ื– ืžืกืคื™ืง ืขืœ ื”ื–ื”ื•ื‘ื™ื
02:57
to guarantee that youโ€™ll win on the silvers?
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ื›ื“ื™ ืœื”ื‘ื˜ื™ื— ืฉืชื–ื›ื• ื‘ื›ืกื•ืคื™ื?
03:01
Hereโ€™s a hint.
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ื”ื ื” ืจืžื–.
03:02
Letโ€™s say at the start of the silver auctions
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ื‘ื•ืื• ื ื’ื™ื“ ืฉื‘ื”ืชื—ืœืช ื”ืžื›ื™ืจื” ืฉืœ ื”ื›ืกื•ืคื™ื
03:05
you had a one gem advantage, such as 9 to 8.
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ื™ืฉ ืœื›ื ื™ืชืจื•ืŸ ืฉืœ ืื‘ืŸ ืื—ื“, ื ื’ื™ื“ 9 ืœ 8.
03:09
You need to win three auctions,
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ืืชื ืฆืจื™ื›ื™ื ืœื–ื›ื•ืช ื‘ืฉืœื•ืฉ ืžื›ื™ืจื•ืช,
03:12
so could you divide your gems into three groups of three and win?
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ืื– ืืชื ื™ื›ื•ืœื™ื ืœื—ืœืง ืืช ื”ืื‘ื ื™ื ืœืฉืœื•ืฉ ืงื‘ื•ืฆื•ืช ืฉืœ ืฉืœื•ืฉ ื•ืœื–ื›ื•ืช?
03:17
For simplicity, letโ€™s assume a set of rules thatโ€™s worse for you,
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ืœืฉื ื”ืคืฉื˜ื•ืช, ื‘ื•ืื• ื ื ื™ื— ืกื˜ ื—ื•ืงื™ื ืฉื’ืจื•ืข ืขื‘ื•ืจื›ื,
03:21
where Gordon wins every tie.
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ื‘ื• ื’ื•ืจื“ื•ืŸ ื–ื•ื›ื” ื‘ื›ืœ ืฉื•ื•ื™ื•ืŸ.
03:24
If you bid 3 each time, the best he could do
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ืื ืืชื ืžืฆื™ืขื™ื 3 ื›ืœ ืคืขื, ื”ื›ื™ ื˜ื•ื‘ ืฉื”ื•ื ื™ื›ื•ืœ ืœืขืฉื•ืช
03:27
is win two silver hexagons, and have two gems leftโ€”
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ื–ื” ืœื–ื›ื•ืช ื‘ืฉื ื™ ืžืฉื•ืฉื™ื ื›ืกื•ืคื™ื, ื•ืฉื™ืฉืืจื• ืœื• ืฉืชื™ ืื‘ื ื™ื --
03:31
which youโ€™ll beat with three bids of 3.
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ืฉืื•ืชืŸ ืชื ืฆื—ื• ืขื ืฉืœื•ืฉ ื”ืฆืขื•ืช ืฉืœ 3.
03:34
Any one-gem advantage where your starting total is divisible by three
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ื›ืœ ื™ืชืจื•ืŸ ืฉืœ ืื‘ืŸ ืื—ืช ื‘ื• ื”ืกืš ื”ื›ื•ืœืœ ืฉืœื›ื ืžืชื—ืœืง ื‘ 3
03:39
will lead to victory by the same logic.
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ื™ื•ื‘ื™ืœ ืœื ืฆื—ื•ืŸ ืœืคื™ ืื•ืชื• ื”ื’ื™ื•ืŸ.
03:43
So knowing that, how can you force Gordon's hand in the gold auctions
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ื‘ื™ื“ื™ืขื” ื”ื–ื•, ืื™ืš ืชื•ื›ืœื• ืœื›ื•ืคืฃ ืืช ื”ื™ื“ ืฉืœ ื’ื•ืจื“ื•ืŸ ื‘ืžื›ื™ืจืช ื”ื–ื”ื•ื‘ื™ื
03:47
so you go into silver with an advantage?
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ื›ืš ืฉืชื›ื ืกื• ืœืืœื• ืฉืœ ื”ื›ืกืฃ ืขื ื™ืชืจื•ืŸ?
03:50
Letโ€™s first imagine that Gordon lets you win the second gold auction
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ื‘ื•ืื• ื ื“ืžื™ื™ืŸ ืงื•ื“ื ืฉื’ื•ืจื“ื•ืŸ ืžืืคืฉืจ ืœื›ื ืœื–ื›ื•ืช ื‘ืžื›ื™ืจืช ื”ื–ื”ื‘ ื”ืฉื ื™ื”
03:54
by betting some amount X with a tie.
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ืขืœ ื™ื“ื™ ื”ื™ืžื•ืจ ืฉืœ ืกื›ื•ื ืžืกื•ื™ื™ื X ื‘ืฉื•ื•ื™ื•ืŸ.
03:58
You could then bid everything you have left on the third gold hexagon,
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ืื– ืชื•ื›ืœื• ืœื”ืฆื™ืข ื›ืœ ืžื” ืฉื ืฉืืจ ืœื›ื ืขืœ ื”ืžืฉื•ืฉื” ื”ืžื•ื–ื”ื‘ ื”ืฉืœื™ืฉื™,
04:02
and he'd have to match you to block.
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ื•ื”ื•ื ื™ื”ื™ื” ื—ื™ื™ื‘ ืœื”ืฉื•ื•ืช ืœื›ื ื›ื“ื™ ืœื—ืกื•ื.
04:05
So if you could bid 51 on the third gold,
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ืื– ืื ืชื•ื›ืœื• ืœื”ืฆื™ืข 51 ืขืœ ื”ื–ื”ื‘ ื”ืฉืœื™ืฉื™,
04:08
you'd go into silver with a 51 to 48 advantage, which you know you can win.
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ืชื™ื›ื ืกื• ืœืžื•ื›ืกืคื™ื ืขื ื™ืชืจื•ืŸ ืฉืœ 51 ืœ 48, ืฉืืชื ื™ื•ื“ืขื™ื ืฉืืชื ื™ื›ื•ืœื™ื ืœื ืฆื—.
04:15
Solving for X reveals that in order to have 51 on round three,
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ืœืคืชื•ืจ ืขื‘ื•ืจ X ืžื’ืœื” ืฉื›ื“ื™ ืฉื™ืฉืืจื• ืœื›ื 51 ื‘ืกื™ื‘ื•ื‘ ื”ืฉืœื™ืฉื™,
04:20
you should bid at most 24 on round two.
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ืืชื ืฆืจื™ื›ื™ื ืœื”ืฆื™ืข ื”ื›ื™ ื”ืจื‘ื” 24 ื‘ืกื™ื‘ื•ื‘ ื”ืฉื ื™.
04:24
But what about the other possibility,
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ืื‘ืœ ืžื” ืขื ื”ืืคืฉืจื•ืช ื”ืฉื ื™ื”,
04:27
where Gordon wins the second gold against your bid of 24โ€”
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ื‘ื” ื’ื•ืจื“ื•ืŸ ื–ื•ื›ื” ื‘ื–ื”ื‘ ื”ืฉื ื™ ืžื•ืœ ื”ื”ืฆืขื” ืฉืœื›ื ืฉืœ 24 --
04:31
would this strategy still work?
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ื”ืื ื”ืืกื˜ืจื˜ื’ื™ื” ื”ื–ื• ืขื“ื™ื™ืŸ ืชืขื‘ื•ื“?
04:34
The least he could bid to win the second gold is 25,
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ื”ื›ื™ ืคื—ื•ืช ืฉื”ื•ื ื™ื›ื•ืœ ืœื”ืฆื™ืข ื›ื“ื™ ืœื–ื›ื•ืช ื‘ื–ื”ื‘ ื”ืฉื ื™ ื–ื” 25,
04:38
making the total 75 to Gordonโ€™s 74.
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ืžื” ืฉืขื•ืฉื” ืืช ืกืš ื”ื›ื•ืœ 75 ืœ 74 ืฉืœ ื’ื•ืจื“ื•ืŸ.
04:42
No one would then bid on round three,
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ืืฃ ืื—ื“ ืœื ื™ืฆื™ืข ืื– ื‘ืกื™ื‘ื•ื‘ ื”ืฉืœื™ืฉื™,
04:45
since youโ€™ve each blocked the other from getting three golds.
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ืžืื—ืจ ืฉื›ืœ ืื—ื“ ื—ืกื ืืช ื”ืื—ืจ ืžืœื”ื’ื™ืข ืœืฉืœื•ืฉื” ื–ื”ื•ื‘ื™ื.
04:49
After that, you could bid 25 every time to win three silvers.
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ืื—ืจื™ ื–ื”, ืืชื ืชื•ื›ืœื• ืœื”ืฆื™ืข 25 ื›ืœ ืคืขื ื›ื“ื™ ืœื–ื›ื•ืช ื‘ืฉืœื•ืฉืช ื”ื›ืกื•ืคื™ื.
04:55
The bidding war was close,
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ืžืœื—ืžืช ื”ื”ืฆืขื•ืช ื”ื™ืชื” ืงืจื•ื‘ื”,
04:56
but your ingenuity kept you one link ahead in the chain of inference,
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ืื‘ืœ ื”ื—ื•ื›ืžื” ืฉืœื›ื ืฉืžืจื” ืขืœื™ื›ื ื—ื•ืœื™ื” ืื—ืช ืงื“ื™ืžื” ื‘ืฉืจืฉืจืช ื”ื”ืกืงื”,
05:01
and the silver tri-source is yours.
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ื•ื”ืžืงื•ืจ ื”ืžืฉื•ืœืฉ ื”ื›ืกื•ืฃ ืฉืœื›ื.
05:04
Now... what will you do with it?
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ืขื›ืฉื™ื•... ืžื” ืชืขืฉื• ืื™ืชื•?
ื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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