Can you solve the rebel supplies riddle? - Alex Gendler

2,852,855 views ใƒป 2018-09-10

TED-Ed


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

ืชืจื’ื•ื: Shlomo Adam ืขืจื™ื›ื”: Ido Dekkers
00:06
Youโ€™re overseeing the delivery of crucial supplies to a rebel base
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ืืชื ืžืคืงื—ื™ื ืขืœ ืžืฉืœื•ื— ืืกืคืงื” ื“ื—ื•ืคื” ืœื‘ืกื™ืก ื”ืžื•ืจื“ื™ื
00:11
deep in the heart of enemy territory.
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ืฉื‘ืขื•ืžืง ืฉื˜ื— ื”ืื•ื™ื‘.
00:14
To get past Imperial customs, all packages must follow a strict protocol:
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ื›ื“ื™ ืœืขื‘ื•ืจ ืืช ื‘ื™ืงื•ืจืช ื”ืžื›ืก ื”ืงื™ืกืจื™ืช ืขืœ ื›ืœ ื”ื—ื‘ื™ืœื•ืช ืœืขืžื•ื“ ื‘ืชืงื ื•ืŸ ืžื—ืžื™ืจ:
00:19
if a box is marked with an even number on the bottom,
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ื›ืœ ืชื™ื‘ื” ืฉื‘ืชื—ืชื™ืชื” ืžืกืคืจ ื–ื•ื’ื™
00:23
it must be sealed with a red top.
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ืฆืจื™ื›ื” ืœื”ื™ืกื’ืจ ื‘ืžื›ืกื” ืื“ื•ื.
00:27
The boxes are already being loaded onto the transport
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ื”ืชื™ื‘ื•ืช ื›ื‘ืจ ื”ื•ืขืžืกื• ืœืžืฉืœื•ื—
00:30
when you receive an urgent message.
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ื›ืฉืืชื ืชืงื‘ืœื™ื ื”ื•ื“ืขื” ื“ื—ื•ืคื”:
00:32
One of the four boxes was sealed incorrectly,
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ืื—ืช ืžืืจื‘ืข ื”ืชื™ื‘ื•ืช ื›ื•ืกืชื” ื‘ืžื›ืกื” ืฉื’ื•ื™,
00:36
but they lost track of which one.
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ืื‘ืœ ืœื ื‘ืจื•ืจ ืื™ื–ื• ืžื”ืŸ.
00:38
All the boxes are still on the conveyor belt.
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ื›ืœ ื”ืชื™ื‘ื•ืช ื ืžืฆืื•ืช ืขื“ื™ื™ืŸ ืขืœ ื”ืžืกื•ืข.
00:41
Two are facing down: one marked with a four,
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ืฉืชื™ื™ื ืžื•ื ื—ื•ืช ื”ืคื•ืš: ืื—ืช ืฉืžืกืคืจื” ืืจื‘ืข
00:45
and one with a seven.
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ื•ืื—ืช ืฉืžืกืคืจื” ืฉื‘ืข.
00:46
The other two are facing up:
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ืฉืชื™ ื”ืื—ืจื•ืช ืžื•ื ื—ื•ืช ื ื›ื•ืŸ:
00:48
one with a black top,
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ืื—ืช ืขื ืžื›ืกื” ืฉื—ื•ืจ
00:49
another with a red one.
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ื•ืฉื ื™ื” - ืขื ืžื›ืกื” ืื“ื•ื.
00:52
You know that any violation of the protocol
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ื‘ืจื•ืจ ืœื›ื ืฉื›ืœ ื”ืคืจื” ืฉืœ ื”ืชืงื ื•ืŸ
00:54
will get the entire shipment confiscated and put your allies in grave danger.
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ืชื‘ื™ื ืœื”ื—ืจืžืช ื”ืžืฉืœื•ื— ื›ื•ืœื• ื•ืชืกื›ืŸ ืžืื“ ืืช ื‘ืขืœื™-ื‘ืจื™ืชื›ื.
01:00
But any boxes you pull off for inspection wonโ€™t make it onto this delivery run,
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ืื‘ืœ ื›ืœ ืชื™ื‘ื” ืฉืชืงื—ื• ืžืขืœ ื”ืžืกื•ืข ืœื ืชื’ื™ืข ืœืžืฉืœื•ื— ื”ื ื•ื›ื—ื™
01:05
depriving the rebels of critically needed supplies.
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ื•ืชืžื ืข ืžื”ืžื•ืจื“ื™ื ืืกืคืงื” ืงืจื™ื˜ื™ืช.
01:09
The transport leaves in a few moments, with or without its cargo.
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ื”ืžืฉืœื•ื— ื™ื•ืฆื ื‘ืชื•ืš ื“ืงื•ืช ืื—ื“ื•ืช, ืขื ืื• ื‘ืœื™ ื”ืžื˜ืขืŸ.
01:13
Which box or boxes should you grab off the conveyor belt?
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ืื™ืœื• ืชื™ื‘ื” ืื• ืชื™ื‘ื•ืช ืขืœื™ื›ื ืœืงื—ืช ืžื”ืžืกื•ืข?
ืขื™ืฆืจื• ืืช ื”ืกืจื˜ื•ืŸ ืื ื‘ืจืฆื•ื ื›ื ืœืžืฆื•ื ืืช ื”ืชืฉื•ื‘ื” ื‘ืขืฆืžื›ื!
01:18
Pause the video now if you want to figure it out for yourself!
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ื', ืžืก' ื–ื•ื’ื™=ืžื›ืกื” ืื“ื•ื ื‘', 2 ืชื™ื‘ื•ืช ื”ืคื•ื›ื•ืช: 4 ื•-7
ื’', ืื—ืช ื”ืชื™ื‘ื•ืช ืžืคื™ืจื” ืืช ื›ืœืœ 1 ื“', ื™ืฉ ืœื”ืกื™ืจ ืชื™ื‘ื” ืื—ืช ื‘ืœื‘ื“
01:23
Answer in: 3
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ื”', ืืคืฉืจ ืœืงื—ืช ืจืง ืชื™ื‘ื” ืื—ืช, ืฉืœื ืชื™ืฉืœื—.
01:25
Answer in: 2
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01:26
Answer in: 1
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ืคืชืจื•ืŸ ื‘ืขื•ื“ 3, 2, 1.
01:27
It may seem like you need to inspect all four boxes
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ืœื›ืื•ืจื”, ืขืœื™ื›ื ืœื‘ื“ื•ืง ืืช ื›ืœ ืืจื‘ืข ื”ืชื™ื‘ื•ืช
01:31
to see whatโ€™s on the other side of each.
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ื›ื“ื™ ืœืจืื•ืช ืžื” ื‘ืฆื™ื“ื” ื”ืฉื ื™ ืฉืœ ื›ืœ ืื—ืช ืžื”ืŸ.
01:33
But in fact, only two of them matter.
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ืืš ืœืžืขืฉื”, ืจืง ืฉืชื™ื™ื ืžื”ืŸ ื—ืฉื•ื‘ื•ืช.
01:36
Letโ€™s look at the protocol again.
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ื”ื‘ื” ื•ื ืขื™ื™ืŸ ืฉื•ื‘ ื‘ืชืงื ื•ืŸ.
01:38
All it says is that even-numbered boxes must have a red top.
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ื›ืชื•ื‘ ืฉื ืฉืจืง ืชื™ื‘ื•ืช ืขื ืžืกืคืจ ื–ื•ื’ื™ ืžื—ื•ื™ื™ื‘ื•ืช ื‘ืžื›ืกื” ืื“ื•ื.
01:42
It doesnโ€™t say anything about odd-numbered boxes,
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ืœื ื ืืžืจ ื“ื‘ืจ ืขืœ ืชื™ื‘ื•ืช ืฉืžืกืคืจืŸ ืื™-ื–ื•ื’ื™,
01:45
so we can just ignore the box marked with a seven.
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ืœื›ืŸ ื ื•ื›ืœ ืœื”ืชืขืœื ืžื”ืชื™ื‘ื” ืฉืžืžื•ืกืคืจืช ื‘-7.
01:48
What about the box with a red top?
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ืžื” ืขื ื”ืชื™ื‘ื” ื‘ืขืœืช ื”ืžื›ืกื” ื”ืื“ื•ื?
01:51
Donโ€™t we need to check that the number on the bottom is even?
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ื”ืื ืœื ื›ื“ืื™ ืฉื ื‘ื“ื•ืง ืื ื”ืžืกืคืจ ื‘ืชื—ืชื™ืชื” ื–ื•ื’ื™?
01:54
As it turns out, we donโ€™t.
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ืžืกืชื‘ืจ ืฉืœื.
01:56
The protocol says that if a box has an even number,
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ื”ืชืงื ื•ืŸ ืงื•ื‘ืข ืฉืื ืžืกืคืจ ื”ืชื™ื‘ื” ื”ื•ื ื–ื•ื’ื™,
02:00
then it should have a red top.
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ื”ื™ื ืžื—ื•ื™ื™ื‘ืช ื‘ืžื›ืกื” ืื“ื•ื.
02:02
It doesnโ€™t say that only boxes with even numbers can have red tops,
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ืœื ื ืืžืจ ื‘ื• ืฉืชื™ื‘ื•ืช ื–ื•ื’ื™ื•ืช ื‘ืœื‘ื“ ืžื—ื•ื™ื™ื‘ื•ืช ื‘ืžื›ืกื” ืื“ื•ื,
02:07
or that a box with a red top must have an even number.
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ืื• ืฉืชื™ื‘ื” ื‘ืขืœืช ืžื›ืกื” ืื“ื•ื ืžื—ื•ื™ื™ื‘ืช ื‘ืžืกืคืจ ื–ื•ื’ื™.
02:11
The requirement only goes in one direction.
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ื”ื“ืจื™ืฉื” ื”ื™ื ื‘ื›ื™ื•ื•ืŸ ืื—ื“ ื‘ืœื‘ื“.
02:15
So we donโ€™t need to check the box with the red lid.
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ืœื›ืŸ ืื™ื ื ื• ืฆืจื™ื›ื™ื ืœื‘ื“ื•ืง ืืช ื”ืชื™ื‘ื” ื‘ืขืœืช ื”ืžื›ืกื” ื”ืื“ื•ื.
02:17
We do, however, need to check the one with the black lid,
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ืื‘ืœ ืขืœื™ื ื• ืœื‘ื“ื•ืง ืืช ื–ื• ืฉื”ืžื›ืกื” ืฉืœื” ืฉื—ื•ืจ
02:21
to make sure it wasnโ€™t incorrectly placed on an even-numbered box.
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ื›ื“ื™ ืœื•ื•ื“ื ืฉื”ื•ื ืœื ื”ื•ื ื— ื‘ื˜ืขื•ืช ืขืœ ืชื™ื‘ื” ืฉืžืกืคืจื” ื–ื•ื’ื™.
02:26
If you initially assumed the rules imply a symmetrical match
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ืื ื”ื ื—ืชื ืžืœื›ืชื—ื™ืœื” ืฉื”ื›ืœืœื™ื ืžื•ืจื™ื ืขืœ ื”ืชืืžื” ืกื™ืžื˜ืจื™ืช
ื‘ื™ืŸ ืžืกืคืจ ื”ืชื™ื‘ื” ืœืฆื‘ืข ื”ืžื›ืกื”, ืื™ื ื›ื ืœื‘ื“.
02:30
between the number on the box and the type of lid, youโ€™re not alone.
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02:33
That error is so common, we even have a name for it:
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ื”ื˜ืขื•ืช ื”ื™ื ื›ื” ืฉื›ื™ื—ื”, ืฉื”ื™ื ื–ื›ืชื” ืœืฉื ืžืฉืœื”:
02:37
affirming the consequent,
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"ืื™ืฉื•ืจ ื”ืกื•ื’ืจ",
02:39
or the fallacy of the converse.
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ืื• "ื”ื›ืฉืœ ื”ืœื•ื’ื™ ืฉืœ ื”ื”ื™ืคื•ืš".
02:42
This fallacy wrongly assumes
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ื”ื›ืฉืœ ื”ื–ื” ืžื ื™ื— ื‘ื˜ืขื•ืช
02:44
that just because a certain condition is necessary for a given result,
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ืฉืจืง ืžืฉื•ื ืฉืชื ืื™ ืžืกื•ื™ื ื”ื›ืจื—ื™ ืœืชื•ืฆืื” ื ืชื•ื ื”,
02:48
it must also be sufficient for it.
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ื”ื•ื ื’ื ืžืกืคื™ืง ื›ื“ื™ ืœื”ืฉื™ื’ื”.
02:51
For instance, having an atmosphere is a necessary condition
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ืœืžืฉืœ, ืื˜ืžื•ืกืคื™ืจื” ื”ื™ื ืชื ืื™ ื”ื›ืจื—ื™
02:54
for being a habitable planet.
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ืœื›ื•ื›ื‘-ืœื›ืช ืจืื•ื™ ืœืžื—ื™ื™ื”.
02:56
But this doesnโ€™t mean that itโ€™s a sufficient condition โ€“
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ืื‘ืœ ืื™ืŸ ื–ื” ืื•ืžืจ ืฉื”ื™ื ื”ืชื ืื™ ื”ื™ื—ื™ื“ -
02:59
planets like Venus have atmospheres but lack other criteria for habitability.
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ื‘ื›ื•ื›ื‘ื™-ืœื›ืช ื›ืžื• ื ื•ื’ื” ื™ืฉ ืื˜ืžื•ืกืคื™ืจื” ืื‘ืœ ื—ืกืจื™ื ื‘ื”ื ืชื ืื™ื ืื—ืจื™ื ืœืžื—ื™ื™ื”.
03:05
If that still seems hard to wrap your head around,
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ืื ืขื“ื™ื™ืŸ ืงืฉื” ืœื›ื ืœื”ื‘ื™ืŸ ื–ืืช,
03:08
letโ€™s look at a slightly different problem.
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ื”ื‘ื” ื ืชื‘ื•ื ืŸ ื‘ื‘ืขื™ื” ืฉื•ื ื” ื‘ืžืงืฆืช.
03:11
Imagine the boxes contain groceries.
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ื“ืžื™ื™ื ื• ืฉื”ืชื™ื‘ื•ืช ืžื›ื™ืœื•ืช ืžืฆืจื›ื™ ืžื–ื•ืŸ.
03:13
You see one marked for shipment to a steakhouse
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ืืชื ืจื•ืื™ื ืชื™ื‘ื” ืฉืžืกื•ืžื ืช ืœืžืฉืœื•ื— ืœืžืกืขื“ืช ืกื˜ื™ื™ืงื™ื,
03:16
and one to a vegetarian restaurant.
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ื•ืื—ืจืช - ืœืžืกืขื“ื” ืฆืžื—ื•ื ื™ืช.
03:19
Then you see two more boxes turned upside down:
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ื•ืื– ืืชื ืจื•ืื™ื ืฉืชื™ื™ื ื ื•ืกืคื•ืช ื”ืžื•ื ื—ื•ืช ื”ืคื•ืš:
03:22
one labeled as containing meat,
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ืื—ืช ืžืกื•ืžื ืช ื›ืžื›ื™ืœื” ื‘ืฉืจ,
03:24
and another as containing onions.
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ื•ืื—ืจืช - ื‘ืฆืœื™ื.
03:26
Which ones do you need to check?
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ืื™ื–ื• ืžื”ืŸ ืขืœื™ื›ื ืœื‘ื“ื•ืง?
ื•ื‘ื›ืŸ, ื–ื” ืงืœ -
03:29
Well, itโ€™s easy โ€“
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03:30
make sure the meat isnโ€™t being shipped to the vegetarian restaurant,
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ื•ื“ืื• ืฉื”ื‘ืฉืจ ืœื ื™ื™ืฉืœื— ืœืžืกืขื“ื” ื”ืฆืžื—ื•ื ื™ืช,
03:33
and that the box going there doesnโ€™t contain meat.
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ื•ืฉื”ืชื™ื‘ื” ื”ืžื™ื•ืขื“ืช ืœืฉื ืœื ืžื›ื™ืœื” ื‘ืฉืจ.
03:37
The onions can go to either place,
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ื”ื‘ืฆืœื™ื ื™ื›ื•ืœื™ื ืœื”ื™ืฉืœื— ืœื–ื• ื•ื’ื ืœื–ื•,
03:39
and the box bound for the steakhouse can contain either product.
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ื•ื”ืชื™ื‘ื” ืฉืžื™ื•ืขื“ืช ืœืžืกืขื“ืช ื”ืกื˜ื™ื™ืงื™ื ื™ื›ื•ืœื” ืœื”ื›ื™ืœ ืืช ืฉื ื™ ื”ืžื•ืฆืจื™ื.
03:43
Why does this scenario seem easier?
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ืžื“ื•ืข ื”ืชืจื—ื™ืฉ ื”ื–ื” ื ืจืื” ืงืœ ื™ื•ืชืจ?
03:45
Formally, itโ€™s the same problem โ€“
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ืจืฉืžื™ืช, ื–ื• ืื•ืชื” ื”ื‘ืขื™ื” -
03:47
two possible conditions for the top of the box,
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ืฉื ื™ ืชื ืื™ื ืืคืฉืจื™ื™ื ื‘ื ื•ื’ืข ืœืžื›ืกื” ื”ืชื™ื‘ื”,
03:50
and two for the bottom.
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ื•ืฉื ื™ื™ื - ื‘ื ื•ื’ืข ืœืชื—ืชื™ืชื”.
03:51
But in this case, theyโ€™re based on familiar real-world needs,
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ืืœื ืฉื‘ืžืงืจื” ื–ื” ื”ื ืžื‘ื•ืกืกื™ื ืขืœ ืฆืจื›ื™ื ืžื•ื›ืจื™ื,
03:55
and we easily understand that while vegetarians only eat vegetables,
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ื•ืงืœ ืœื ื• ืœื”ื‘ื™ืŸ ืฉื‘ืขื•ื“ ืฉืฆืžื—ื•ื ื™ื ืื•ื›ืœื™ื ื™ืจืงื•ืช ื‘ืœื‘ื“,
03:59
theyโ€™re not the only ones who do so.
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ื”ื ืื™ื ื ื”ื™ื—ื™ื“ื™ื.
04:02
In the original problem, the rules seemed more arbitrary,
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ื‘ื‘ืขื™ื” ื”ืžืงื•ืจื™ืช ื”ื›ืœืœื™ื ื ืจืื™ื ืฉืจื™ืจื•ืชื™ื™ื ื™ื•ืชืจ,
04:05
and when theyโ€™re abstracted that way,
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ื•ื›ืฉื”ื ืžื•ืฆื’ื™ื ื‘ืื•ืคืŸ ืžื•ืคืฉื˜ ื›ื–ื”,
04:08
the logical connections become harder to see.
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ืงืฉื” ื™ื•ืชืจ ืœืจืื•ืช ืืช ื”ืงืฉืจื™ื ื”ืœื•ื’ื™ื™ื.
04:11
In your case, youโ€™ve managed to get enough supplies through
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ื‘ืžืงืจื” ืฉืœื›ื, ื”ืฆืœื—ืชื ืœืฉืœื•ื— ื“ื™ ืืกืคืงื”
04:14
to enable the resistance to fight another day.
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ื›ื“ื™ ืœืืคืฉืจ ืœืžื—ืชืจืช ื™ื•ื ืœื—ื™ืžื” ื ื•ืกืฃ.
04:17
And you did it by thinking outside the box โ€“
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ื•ืืช ื–ื” ืขืฉื™ืชื ื‘"ื—ืฉื™ื‘ื” ืžื—ื•ืฅ ืœืชื™ื‘ื”"...
04:20
both sides of it.
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ืžื—ื•ืฅ ืœืฉื ื™ ืฆื™ื“ื™ื”.
ื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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