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Sci Show
Why Are There So Many Species Near the Equator?
Can You Solve The 25 Horses Puzzle? Google Interview Question
There are 25 mechanical horses and a single racetrack. Each horse completes the track in a pre-programmed time, and the horses all have different finishing times, unknown to you. You can race 5 horses at a time. After a race is over, you get a printout with the order the horses finished, but not the finishing times of the horses. What is the minimum number of races you need to identify the fastest 3 horses?

I was suggested this puzzle via email by Terry Stickels. This is also a popular interview question at tech companies like Google. See a list of all sources in my blog post for this video:
https://wp.me/p6aMk-58P

If you like my videos, you can support me at Patreon: http://www.patreon.com/mindyourdecisions

Connect on social media. I update each site when I have a new video or blog post, so you can follow me on whichever method is most convenient for you.

My Blog: http://mindyourdecisions.com/blog/
Twitter: http://twitter.com/preshtalwalkar
Facebook: https://www.facebook.com/pages/Mind-Your-Decisions/168446714965
Google+: https://plus.google.com/108336608566588374147/posts
Pinterest: https://www.pinterest.com/preshtalwalkar/
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Instagram: https://instagram.com/preshtalwalkar/
Patreon: http://www.patreon.com/mindyourdecisions

Newsletter (sent about 2 times a year): http://eepurl.com/KvS0r

My Books

"The Joy of Game Theory" shows how you can use math to out-think your competition. (rated 3.8/5 stars on 27 reviews) https://www.amazon.com/gp/product/1500497444

"The Irrationality Illusion: How To Make Smart Decisions And Overcome Bias" is a handbook that explains the many ways we are biased about decision-making and offers techniques to make smart decisions. (rated 5/5 stars on 2 reviews) https://www.amazon.com/gp/product/1523231467/

"Math Puzzles Volume 1" features classic brain teasers and riddles with complete solutions for problems in counting, geometry, probability, and game theory. Volume 1 is rated 4.4/5 stars on 13 reviews. https://www.amazon.com/gp/product/1517421624/

"Math Puzzles Volume 2" is a sequel book with more great problems. (rated 5/5 stars on 3 reviews) https://www.amazon.com/gp/product/1517531624/

"Math Puzzles Volume 3" is the third in the series. (rated 3.8/5 stars on 4 reviews) https://www.amazon.com/gp/product/1517596351/

"40 Paradoxes in Logic, Probability, and Game Theory" contains thought-provoking and counter-intuitive results. (rated 4.7/5 stars on 12 reviews) https://www.amazon.com/gp/product/1517319307/

"The Best Mental Math Tricks" teaches how you can look like a math genius by solving problems in your head (rated 4.7/5 stars on 4 reviews) https://www.amazon.com/gp/product/150779651X/

"Multiply Numbers By Drawing Lines" This book is a reference guide for my video that has over 1 million views on a geometric method to multiply numbers. (rated 5/5 stars on 3 reviews) https://www.amazon.com/gp/product/1500866148/
TODAY



Big Think
2017-07-22 17:00
Why You Should Read Philosophy: Truth, Knowledge, and Meaning
Why You Should Read Philosophy: Truth, Knowledge, and Meaning
Austin Evans
2017-07-22 16:03
Photon 3.0 $500 Gaming PC Build (2017)
Photon 3.0 $500 Gaming PC Build (2017)
Wranglestar
2017-07-22 11:21
How To Build A Bridge Over A Creek For A Tractor 6
How To Build A Bridge Over A Creek For A Tractor 6
TWiT Netcast Network
2017-07-22 02:41
Dark Web Whack-A-Mole
Dark Web Whack-A-Mole
Electronics Engineering
2017-07-22 02:32
EEVacademy #4 -  I²C (I2C) Bit Banging
EEVacademy #4 - I²C (I2C) Bit Banging
YESTERDAY
CNET TV
2017-07-21 22:34
'The Walking Dead' season 8 trailer debuts at Comic-Con
'The Walking Dead' season 8 trailer debuts at Comic-Con
Sci Show
2017-07-21 21:00
Should You Worry About Antarctica's New, Massive Iceberg?
Should You Worry About Antarctica's New, Massive Iceberg?
Henders 007
2017-07-21 19:35
Tim's Dual Purpose Toys
Tim's Dual Purpose Toys
NASA Television
2017-07-21 19:16
Happy 100th Anniversary, Langley on This Week @NASA – July 21, 2017
Happy 100th Anniversary, Langley on This Week @NASA – July 21, 2017
How Stuff Works
2017-07-21 17:00
Yogurt: More Than Just Bacteria Poop | FoodStuff
Yogurt: More Than Just Bacteria Poop | FoodStuff
3Blue1Brown
2017-07-21 15:33
Hilbert's Curve: Is infinite math useful? (Update with improved audio)
Hilbert's Curve: Is infinite math useful? (Update with improved audio)
TEDTalks
2017-07-21 15:14
Why design should include everyone | Sinéad Burke
Why design should include everyone | Sinéad Burke
The Khan Academy
2017-07-21 15:11
Differentiability and continuity
Differentiability and continuity
Tested
2017-07-21 14:00
PROJECTIONS, Episode 18: Marvel Powers United VR, Oculus Interview
PROJECTIONS, Episode 18: Marvel Powers United VR, Oculus Interview
NASA Goddard
2017-07-21 13:06
GLOBE Observer Eclipse App
GLOBE Observer Eclipse App
Android Authority
2017-07-21 12:58
Nokia 6 hands on
Nokia 6 hands on
Matthias Wandel
2017-07-21 11:00
Making wood thread taps
Making wood thread taps
BigcLiveDotCom
2017-07-21 08:21
Are over-discharged lithium cells safe?  (And how to test for damage.)
Are over-discharged lithium cells safe? (And how to test for damage.)
TWiT Netcast Network
2017-07-21 01:19
Elon Musk's Boring Tube
Elon Musk's Boring Tube
The Khan Academy
2017-07-21 01:02
Estimating derivative at a point
Estimating derivative at a point
2017-07-20



Grant Thompson - "The King of Random"
2017-07-20 22:06
We Made Mark Rober's World's Largest Super Soaker!
We Made Mark Rober's World's Largest Super Soaker!
Stanford University
2017-07-20 21:57
Humpback whale flapping foreflipper
Humpback whale flapping foreflipper
Wranglestar
2017-07-20 21:53
Are You Disorganized? How To FIX IT!!!
Are You Disorganized? How To FIX IT!!!
Sci Show
2017-07-20 21:00
Conservation Genomics and Kizmit the Porcupine: SciShow Talk Show
Conservation Genomics and Kizmit the Porcupine: SciShow Talk Show
MindYourDecisions
2017-07-20 20:45
What is 48÷2(9+3) = ? The Correct Answer Explained
What is 48÷2(9+3) = ? The Correct Answer Explained
Computerphile
2017-07-20 20:41
Now Hiring? (What Computing Companies Look For) - Computerphile
Now Hiring? (What Computing Companies Look For) - Computerphile
Computer World
2017-07-20 20:09
Tech Talk: The latest on Azure Stack, cyberattacks, the next iPhone and ... keyboards
Tech Talk: The latest on Azure Stack, cyberattacks, the next iPhone and ... keyboards
Linus Tech Tips
2017-07-20 19:04
A Wireless Mouse That Lasts FOREVER! - HOLY $H!T Ep. 20
A Wireless Mouse That Lasts FOREVER! - HOLY $H!T Ep. 20
NASA Goddard
2017-07-20 18:38
A New View of August's Total Solar Eclipse
A New View of August's Total Solar Eclipse
CNET TV
2017-07-20 17:53
Elon Musk says NY-DC hyperloop is coming
Elon Musk says NY-DC hyperloop is coming
Big Think
2017-07-20 17:28
Optimists Do It Longer: How a Positive Outlook Will Boost Your Longevity | Michael Scheier
Optimists Do It Longer: How a Positive Outlook Will Boost Your Longevity | Michael Scheier
I Like To Make Stuff
2017-07-20 15:30
How to make a Guitar Case // Woodworking
How to make a Guitar Case // Woodworking
Cody´s Lab
2017-07-20 14:41
Gardening With Cody 12017 Week 14: First Harvest
Gardening With Cody 12017 Week 14: First Harvest
Tested
2017-07-20 14:00
Making The Lich King Armor for Blizzard!
Making The Lich King Armor for Blizzard!
MinutePhysics
2017-07-20 14:00
What Is The Shape of Space? (ft. PhD Comics)
What Is The Shape of Space? (ft. PhD Comics)
Deep Sky Videos
2017-07-20 11:09
Black Eye Galaxy (M64) - Deep Sky Videos
Black Eye Galaxy (M64) - Deep Sky Videos
Android Authority
2017-07-20 09:37
Some OnePlus 5 units reboot when dialing 911: What to do about it!
Some OnePlus 5 units reboot when dialing 911: What to do about it!
AvE
2017-07-20 05:24
Pyrolized Bread Metal Casting Foundry.
Pyrolized Bread Metal Casting Foundry.
TWiT Netcast Network
2017-07-20 02:05
Musicals Are Branching Out into Podcasting
Musicals Are Branching Out into Podcasting
MAKE Magazine
2017-07-20 00:03
Make: Live - Arduino Traffic Tracker
Make: Live - Arduino Traffic Tracker
2017-07-19
BigcLiveDotCom
2017-07-19 20:22
Mailbag style video with stuff from the Glasgow meet-up.
Mailbag style video with stuff from the Glasgow meet-up.
Wranglestar
2017-07-19 20:18
Renovating The Old Pole Barn - BEFORE & AFTER
Renovating The Old Pole Barn - BEFORE & AFTER
Standpmaths
2017-07-19 19:06
Brilliant Geometry: a physical 3D zoetrope of a 4D cube
Brilliant Geometry: a physical 3D zoetrope of a 4D cube
Linus Tech Tips
2017-07-19 18:45
5 Ways to Watch 4K Content on the PC
5 Ways to Watch 4K Content on the PC
Stanford University
2017-07-19 18:22
Stanford researchers develop vine-like, growing robot
Stanford researchers develop vine-like, growing robot
The Khan Academy
2017-07-19 17:12
Derivative as a concept
Derivative as a concept
Big Think
2017-07-19 17:00
Which Jobs Will Machines Take Over? Movie Critics, Doctors, Truckers...
Which Jobs Will Machines Take Over? Movie Critics, Doctors, Truckers...
ElectroBOOM
2017-07-19 16:28
Dangers of Using Electronics in Bathroom, the Case of the Teenage Girl
Dangers of Using Electronics in Bathroom, the Case of the Teenage Girl
Austin Evans
2017-07-19 16:18
Is the Nintendo 2DS XL Worth It?
Is the Nintendo 2DS XL Worth It?
Minute Earth
2017-07-19 15:22
Why It Sucks to Be a Male Hyena
Why It Sucks to Be a Male Hyena
TEDTalks
2017-07-19 14:37
Doesn't everyone deserve a chance at a good life? | Jim Yong Kim
Doesn't everyone deserve a chance at a good life? | Jim Yong Kim
The Royal Institution
2017-07-19 14:21
Q&A - The Science of Stress: From Psychology to Physiology
Q&A - The Science of Stress: From Psychology to Physiology
The Royal Institution
2017-07-19 14:20
The Science of Stress: From Psychology to Physiology
The Science of Stress: From Psychology to Physiology
Tested
2017-07-19 14:00
Making a Star Wars Battlefront 2 Helmet for Janina Gavankar!
Making a Star Wars Battlefront 2 Helmet for Janina Gavankar!
Numberphile
2017-07-19 13:26
Large Gaps between Primes - Numberphile
Large Gaps between Primes - Numberphile
CNET TV
2017-07-19 13:07
Google Glass is back, Bluetooth to work over mesh networks
Google Glass is back, Bluetooth to work over mesh networks
Electronics Engineering
2017-07-19 05:39
EEVblog #1008 - Mystery Teardown
EEVblog #1008 - Mystery Teardown
TWiT Netcast Network
2017-07-19 05:18
Retiring Emoji Blobs
Retiring Emoji Blobs
2017-07-18
Sci Show
2017-07-18 21:00
Why Are Belly Flops So Painful?
Why Are Belly Flops So Painful?
Marques Brownlee
2017-07-18 20:35
Galaxy Note... Fan Edition? Ask MKBHD V18!
Galaxy Note... Fan Edition? Ask MKBHD V18!
Linus Tech Tips
2017-07-18 18:59
WTF?? A 3-Dimensional Keyboard??
WTF?? A 3-Dimensional Keyboard??
Grant Thompson - "The King of Random"
2017-07-18 18:00
Experiment: Charcoal and High Voltage
Experiment: Charcoal and High Voltage
TEDTalks
2017-07-18 17:56
How your brain hallucinates your conscious reality | Anil Seth
How your brain hallucinates your conscious reality | Anil Seth
Big Think
2017-07-18 17:00
Knowing How to Tell a Good Story Is Like Having Mind Control | Alan Alda
Knowing How to Tell a Good Story Is Like Having Mind Control | Alan Alda
The Verge
2017-07-18 13:00
How Dolby is measuring human emotions to hack Hollywood | Next Level Ep. 2
How Dolby is measuring human emotions to hack Hollywood | Next Level Ep. 2
Wranglestar
2017-07-18 02:20
I'm Building Men, Not Snowflakes
I'm Building Men, Not Snowflakes
TWiT Netcast Network
2017-07-18 01:26
Are You Addicted to Your Smartphone?
Are You Addicted to Your Smartphone?
2017-07-17
CNET TV
2017-07-17 23:31
How to hide the navigation bar on the Galaxy S (CNET How To)
How to hide the navigation bar on the Galaxy S (CNET How To)
Sci Show
2017-07-17 21:00
The Fog That Killed 12,000 People
The Fog That Killed 12,000 People
TEDTalks
2017-07-17 19:33
When I die, recompose me | Katrina Spade
When I die, recompose me | Katrina Spade
Linus Tech Tips
2017-07-17 18:59
Cheap $45 Mechanical Keyboard Round Up!
Cheap $45 Mechanical Keyboard Round Up!
NASA Goddard
2017-07-17 17:03
NICER in Space
NICER in Space
Big Think
2017-07-17 17:00
Why Interest-Based Negotiation Will Get You What You Really Want
Why Interest-Based Negotiation Will Get You What You Really Want
NASA Television
2017-07-17 16:45
Expedition 52-53 Crew Departs for Kazakh Launch Site
Expedition 52-53 Crew Departs for Kazakh Launch Site
The Khan Academy
2017-07-17 16:31
Limits of trigonometric functions
Limits of trigonometric functions
Vsauce
2017-07-17 15:37
How Much of the Earth Can You See at Once?
How Much of the Earth Can You See at Once?
Android Authority
2017-07-17 15:18
Sorry folks, Facebook Messenger ads are rolling out globally
Sorry folks, Facebook Messenger ads are rolling out globally
NASA Television
2017-07-17 15:16
Celebrating 100 Years of NASA Langley: A Storied Legacy, A Soaring Future
Celebrating 100 Years of NASA Langley: A Storied Legacy, A Soaring Future
Tested
2017-07-17 14:00
Adam Savage's Maker Tour: MIT's Center for Bits and Atoms (Part 2)
Adam Savage's Maker Tour: MIT's Center for Bits and Atoms (Part 2)
Android Authority
2017-07-17 13:31
This is Amazon Alexa on the HTC U11
This is Amazon Alexa on the HTC U11
Periodic Table of Videos
2017-07-17 12:18
World's Saltiest Water - Periodic Table of Videos
World's Saltiest Water - Periodic Table of Videos
BigcLiveDotCom
2017-07-17 11:34
Quest for the shittiest battery charger continues.  (schematic)
Quest for the shittiest battery charger continues. (schematic)
CNET TV
2017-07-17 07:53
Top 5 weird dating apps
Top 5 weird dating apps
AvE
2017-07-17 02:40
High Speed Prototyping
High Speed Prototyping
2017-07-16
Android Authority
2017-07-16 22:08
Nubia Z17 hands-on: the $410 flagship from China
Nubia Z17 hands-on: the $410 flagship from China
TWiT Netcast Network
2017-07-16 21:18
Echo Show Tips
Echo Show Tips
Sci Show
2017-07-16 21:00
Viroids: Possibly the Smallest Pathogens on Earth
Viroids: Possibly the Smallest Pathogens on Earth
MindYourDecisions
2017-07-16 20:25
Can You Solve The Identical Twins Riddle? Paradoxical Probability Puzzle
Can You Solve The Identical Twins Riddle? Paradoxical Probability Puzzle
Computerphile
2017-07-16 19:55
Reason for ARM (Acorn Archimedes at 30) - Computerphile
Reason for ARM (Acorn Archimedes at 30) - Computerphile
Linus Tech Tips
2017-07-16 19:01
The TINIEST Nvidia SLI Setup EVER?
The TINIEST Nvidia SLI Setup EVER?
Big Think
2017-07-16 17:00
Why Are Nations So Divided? Trump, Brexit, and the Struggle for Status
Why Are Nations So Divided? Trump, Brexit, and the Struggle for Status
GreatScott
2017-07-16 14:58
Electronic Basics #30: Microcontroller (Arduino) Timers
Electronic Basics #30: Microcontroller (Arduino) Timers
RedKB
2017-07-16 14:30
Nemesis - Trying to Solve a Bandaged Cube
Nemesis - Trying to Solve a Bandaged Cube
Mr Carlsons Lab
2017-07-16 08:41
Bizarre Circuit Tests Capacitors with RF!
Bizarre Circuit Tests Capacitors with RF!
Wranglestar
2017-07-16 06:31
Testing The Cheapest Knife On AMAZON
Testing The Cheapest Knife On AMAZON
Marques Brownlee
2017-07-16 03:47
Nest Cam IQ: Security Camera + 4k Sensor?
Nest Cam IQ: Security Camera + 4k Sensor?
2017-07-15
Sci Show
2017-07-15 21:00
Why Do Cat Eyes Glow in the Dark?
Why Do Cat Eyes Glow in the Dark?
Big Think
2017-07-15 17:00
How a False Arrest Pushed Ex-Tennis Pro James Blake to Be a Voice for Police Accountability
How a False Arrest Pushed Ex-Tennis Pro James Blake to Be a Voice for Police Accountability
Cody´s Lab
2017-07-15 16:44
Can You Float a Liquid on a Gas?
Can You Float a Liquid on a Gas?
Austin Evans
2017-07-15 16:05
Can You Game on a $400 Laptop?
Can You Game on a $400 Laptop?
How Stuff Works
2017-07-15 16:00
Tonic Syrup: From Curative to Cocktails | FoodStuff
Tonic Syrup: From Curative to Cocktails | FoodStuff
MAKE Magazine
2017-07-15 15:00
Build a Tiny Trebuchet with One Car Workshop
Build a Tiny Trebuchet with One Car Workshop
AvE
2017-07-15 14:00
BOLTR: PROXXON Carving Tool | Germany
BOLTR: PROXXON Carving Tool | Germany
CNET TV
2017-07-15 12:54
Oculus Rift and Touch get price cuts, Microsoft to bring broadband to US
Oculus Rift and Touch get price cuts, Microsoft to bring broadband to US
Grant Thompson - "The King of Random"
2017-07-15 11:00
Lighting off 450 Smoke Bombs
Lighting off 450 Smoke Bombs
Android Authority
2017-07-15 08:47
LG V30: New render shows change in LG's strategy
LG V30: New render shows change in LG's strategy
Tested
2017-07-15 08:03
FartBus.co - This is Only a Test 407 - 7/14/17
FartBus.co - This is Only a Test 407 - 7/14/17
Linus Tech Tips
2017-07-15 04:10
Intel is LOSING its DIGNITY - WAN Show July 14, 2017
Intel is LOSING its DIGNITY - WAN Show July 14, 2017
AvE
2017-07-15 03:30
DERPY DOG LOVES VEGGIES!
DERPY DOG LOVES VEGGIES!
TWiT Netcast Network
2017-07-15 02:00
Little Knobs for the Net
Little Knobs for the Net
BigcLiveDotCom
2017-07-15 01:48
Test of a PSU like the one that went on fire.
Test of a PSU like the one that went on fire.
Electronics Engineering
2017-07-15 00:56
EEVblog #1007 - Is a $25 Multimeter Any Good?
EEVblog #1007 - Is a $25 Multimeter Any Good?
Wranglestar
2017-07-15 00:34
DESTRUCTION TEST - Brush Hog vs Steel Rod
DESTRUCTION TEST - Brush Hog vs Steel Rod
The Khan Academy
2017-07-15 00:14
Analyzing the difference in distributions
Analyzing the difference in distributions
2017-07-14
CNET TV
2017-07-14 22:21
Downgrade from iOS 11 public beta to iOS 10
Downgrade from iOS 11 public beta to iOS 10
Sci Show
2017-07-14 21:00
Meet CERN's New Particle: A Double-Charm Baryon!
Meet CERN's New Particle: A Double-Charm Baryon!
The Khan Academy
2017-07-14 19:32
Example transforming a discrete random variable
Example transforming a discrete random variable
NASA Television
2017-07-14 18:13
Juno Spies Jupiter’s Great Red Spot on This Week @NASA – July 14, 2017
Juno Spies Jupiter’s Great Red Spot on This Week @NASA – July 14, 2017
The Khan Academy
2017-07-14 18:10
Analyzing distribution of sum of two normally distributed random variables
Analyzing distribution of sum of two normally distributed random variables
Steve Ramsey
2017-07-14 18:08
How to reinforce miter joints with super-strong splines. Simple woodworking jig.
How to reinforce miter joints with super-strong splines. Simple woodworking jig.
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