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Can you solve the river crossing riddle? – Lisa Winer

Can you solve the river crossing riddle? – Lisa Winer


As a wildfire rages through
the grasslands, three lions and three wildebeest
flee for their lives. To escape the inferno, they must cross over to the left bank
of a crocodile-infested river. Fortunately, there happens
to be a raft nearby. It can carry up to two animals at a time, and needs as least one lion
or wildebeest on board to row it across the river. There’s just one problem. If the lions ever outnumber the
wildebeest on either side of the river, even for a moment, their instincts will kick in,
and the results won’t be pretty. That includes the animals in the boat
when it’s on a given side of the river. What’s the fastest way for all six animals
to get across without the lions stopping for dinner? Pause here if you want
to figure it out for yourself. Answer in: 3 Answer in: 2 Answer in: 1 If you feel stuck on a problem like this, try listing all the decisions you can make
at each point, and the consequences each choice
leads to. For instance, there are five options
for who goes across first: one wildebeest, one lion, two wildebeest, two lions, or one of each. If one animal goes alone, it’ll just have to come straight back. And if two wildebeest cross first, the remaining one will immediately
get eaten. So those options are all out. Sending two lions, or one of each animal, can actually both lead to solutions
in the same number of moves. For the sake of time,
we’ll focus on the second one. One of each animal crosses. Now, if the wildebeest stays
and the lion returns, there will be three lions
on the right bank. Bad news for the two remaining wildebeest. So we need to have the lion
stay on the left bank and the wildebeest go back to the right. Now we have the same five options, but with one lion
already on the left bank. If two wildebeest go,
the one that stays will get eaten, and if one of each animal goes, the wildebeest on the raft
will be outnumbered as soon as it reaches the other side. So that’s a dead end, which means that at the third crossing, only the two lions can go. One gets dropped off, leaving two lions on the left bank. The third lion takes the raft back to
the right bank where the wildebeest are waiting. What now? Well, since we’ve got two lions waiting
on the left bank, the only option is for two wildebeest
to cross. Next, there’s no sense in two wildebeest
going back, since that just reverses the last step. And if two lions go back, they’ll outnumber the wildebeest
on the right bank. So one lion and one wildebeest
take the raft back leaving us with one of each animal
on the left bank and two of each on the right. Again, there’s no point in sending
the lion-wildebeest pair back, so the next trip should be either
a pair of lions or a pair of wildebeest. If the lions go, they’d eat the wildebeest
on the left, so they stay, and the two wildebeest cross instead. Now we’re quite close because the
wildebeest are all where they need to be with safety in numbers. All that’s left is for that one lion
to raft back and bring his fellow lions over
one by one. That makes eleven trips total, the smallest number needed
to get everyone across safely. The solution that involves sending both
lions on the first step works similarly, and also takes eleven crossings. The six animals escape unharmed
from the fire just in time and begin their new lives
across the river. Of course, now that the danger’s passed, it remains to be seen how long their
unlikely alliance will last.

Comments (100)

  1. Atleast there wasn't a hidden rule or condition that made solution difficult.
    They didn't bend any rules here!

  2. 1 wildabeast 1 lion and 1 wildabeast 1lion and at least the least remaining two

  3. Dude . We have to feed the crocodile sometimes .

  4. Boi its ez!
    Put the carabao and lion 2 by 2 and done!

  5. If the lion is so friendly with the wilderbeast, that they return to bring them, why would they eat them?

  6. 3 moves.
    1. Beest
    2.Kick back.
    3. Repeat with all animals.

  7. Ted: Throw question
    Me: "Alright animals I'll give u guys a minute to disguess"
    "Roar" "Moan" "Roar Roar" "Moan~"
    "For hell's sake I'll save the crocs"
    Lmao~

  8. I choose…
    All will die becouse they cant paddle a boat
    Im so smart ;D

  9. Nostalgia! Solved a similar puzzle with 3 priests and 3 devils crossing the river 15 years ago..

  10. I did this in no time.
    I liked this

  11. Itโ€™s wildebeest lion the wildebeest lion and wildebeest lion

  12. ahaha i actually did it

  13. I have solved it in 9 trips. So the minimum number of trips is 9 not 11. I can challenge that

  14. All your need to do is be Jesus and your done

  15. I only took 9 steps..how is eleven the shortest amount

  16. I SOLVED IT!!!!!!!!!

  17. Just call a swedish minecraft boi, trust me.

  18. it's time the idiots that make up riddles and "problems" understood that intelligence is designed to solve things that NEED to be solved . if an intelligent mind looks at a fake nonsensical problem , it will be dismissed accordingly .

  19. wait, for 1. why didn't the fire get factored into this, was it just waiting for them for 11 TRIPS?
    2.why would lions and prey work together in the first place?
    3. HOW IS A WOOD RAFT WITH A LOT OF WEIGHT ON IT SAFE FROM CROCODILES?

  20. Wait…what's wrong with taking a lion & wildebeast pair across without having to return any on the trip back??…

  21. If they're smart enough to use a raft and work together, they're smart enough to not eat

  22. 3:53
    I SWEAR TO GOD IF YOU EAT THEM AFTER ALL THAT WORK I DID I'M LETTING YOU GET EATEN BY THE CROCS

  23. Thereโ€™s a random raft that all animals can move

  24. I love how the animals just wave all friendly-like even as they're running for their lives from a fire

  25. 1 l W
    2 w w
    3 w w
    4 l l
    5 l l

  26. Ah yes, a raging fire next to a wooden raft! What could possibly go wrong?

  27. No theres a mininum is 4. cause I lion and wilderbeast for 3 times

  28. All I know is Runescape helped me solve this problem

  29. The least number of crosses is 7 not 11

  30. Thank you professor Layton for teaching me a similar puzzle to this

  31. Somehow, I solved it in 9

  32. Humans: can't solve easy riddles
    Animals: know how to operate a raft and work together

  33. I did this in my class and I won its actually simple

  34. so who juss go drop the answer next time??

  35. I did it the other way, with 2 lions on the first crossing

  36. Me during the riddle: i can just put two of each three times
    thinks it over
    Me: yea im right
    thinks it again
    Me im still right

    watches answer

    Me: oh yea the boat still has to get back

  37. I had solved this riddle

  38. Oh wow, now animals know math and how to row boats

  39. Am I the only one who thinks the lions are kind of cute?

  40. Solved it ๐Ÿ™‚

  41. I solved it but I did it using the 2 lions first

  42. Also the answer for the second way is bring 2 lion across
    Bring one back
    Bring 2 lion across
    Bring one back
    Bring 2 wildebeest across
    Bring a wildebeest and lion back
    Bring 2 wildebeest
    Bring a lion back
    Bring 2 lions
    Bring a wildebeest back
    Then finally bring wildebeest and lion across

  43. If the wildebeest outnumber the lions, can the wildebeest gang on the lions and neutralize them or something?

  44. i figured out the lion one without cheating

  45. Is this riddle is also from profesor layton

  46. Me: to lions
    GaRrY tHiS iS A sUrViVaL sItUaTiOn, hOlD iT fOr jUsT tEn mInUtEs

  47. My teacher kinda used this but different :/

    only 1 girl and 3 boys :/

    If the crocodile sees the boys then they will die but the girls wonโ€™t die

  48. If the Lions and wildebeest are able to cooperate, the why don't the crocodiles let the animals jump across their backs?

  49. I'm pretty sure I solved this one, but I used the double lion method and I don't want to go through the process of all 11 trips on the graphic they gave so I'm just assuming I didn't miss anything.

  50. when you actually get it without help, i mean it took 30 min but at least it happened

  51. Just jump on the alligator

  52. My solution: train the crocodiles
    If you donโ€™t know how to watch how to train your dragon
    Crocodiles are pretty much dragons right?

  53. Ted ed : lions feast on wildbeasts once they outnumber them
    Lions : wave to wild beasts !

  54. ….. assuming that
    1. lions would think twice before eating them
    2. the fire wonโ€™t already be there by that time
    3. lions and wildebeests can row a raft

  55. Me: Just have them swim

  56. Easy way to solve this:
    -The pack of animals is a binary number, with 1 representing a wildebeest and 0 representing a lion.
    -The right bank currently looks like 111000
    -the left bank is empty
    -there can never be a greater number of zeros then ones one either side
    -1st move
    -right bank: 1110
    -left bank: 00
    -2nd move:
    -right bank: 10
    -left bank: 1100
    -3rd move
    -right bank: 1100
    -left bank: 10
    -4th move
    -right bank: 00
    -left bank: 1110
    -5th and final move
    -right bank:
    -left bank: 111000

  57. This reminds me of a puzzle…

  58. why you escaping me? everyone does ๐Ÿ™
    I just want to give warm welcomes

  59. Now if Frogger has teached me anything…

  60. In crossing 6 why did two animals need to go
    Just send one wildebeest and bring back one Wildebeest then go get lion and bring him to the left

  61. Excuse me,THE FIRE WOULD HAVE SPREAD BY THEN,IF IT DIDNโ€™T SPREAD THEY WOULD NOT HAVE TO CROSS AND WAIT FOR IT TO DIE DOWN

  62. wildebeast have defensive horns

  63. Take one lion and one idek what that is and repeat

  64. It still plays into action gary

  65. Canโ€™t you do two lions then two wilderness then the remaining ones of each on the same boat

  66. Tbh, the wildebeest actually look stronger than the lions.

  67. 1 question, how can lions or beasts steer a raft??? And why don't the crocks eat the animals in the raft???????

  68. whats up with crocodiles

  69. Solution make a alliance with the crocodiles

  70. Solution:
    Crocs become homies with Wildebeest and they carry them over, then they let the lions take the raft. Wildebeest are out of reach, no one dies!

  71. ok so take the 2 lion over in one raft trip then take the 2 wilder beast and then the wilderbeast and lion over Bam im not sure if im wrong correct me tho

  72. My solution: tell the crocodiles to bring the boat back ??

  73. My solution :
    ??<
    ?>
    ??<
    ?>
    There is now 1? and 3?(yeah it's a zebra I know) on the bad side of the river, and 2? on the good side.
    ??< (Leaving one lion with the wildbeest)
    ??>
    Now, there is 1? and 1? on the good side, and 2? and 2? on the bad side.
    ??< (Leaving the two lions alone)
    Now, we can't send back a wilbeest, because it's gonna get eaten if we send it alone, and if we send two it's the same thing but in reverse.
    ?>
    ??<
    ?>
    ??<

    We now have all six animald on the good side of the river.
    Number of crossing: 11
    Casualties: 0

  74. Wait. Those lions have two eyes on one side of their heads, so that must mean they have 4 eyes…?

  75. Step one: confirm you have green eyes

    Step two: ask the fire to leave

  76. Why would the lions bother to help the wildebeests if they can easily have their dinner and work it out themselves?

  77. just let the lions eat the wildebeest who cares

  78. How do wildebest and lions ride boats?

  79. T(trip)1: 2 lions
    T2: 2 wildabeast
    T3: 1 of each

    Ez

  80. I watched it a long long time ago and then it hit me I knew what it was from my mind

  81. ู…ู€ู€ู€ูŠู†? ูŠู€ู€ุฑุญุจ? ุจู€ูŠ? ูŠู€ู€ู€ู€ุถุบู€ู€ู€ุท ู„ุงูŠู€ูƒ?ูˆูŠู€ู€ู€ู€ุฑุงุณู€ู€ู†ู€ูŠ ุฎู€ู€ู€ู€ู€ุงุต ูˆุงุดู€ู€ู€ุชุฑูƒ ุจู‚ู€ู€ู€ู†ุงุชู€ู€ู€ู€ูŠ
    ูˆุงุชู€ู€ู€ุณุงุจ**00212.674.056.812*???

  82. Is no one going to acknowledge the fact that wildebeest and lions can operate rafts?

  83. I know I actually could solve this and I tried but…

  84. The real riddle here is wtf is a wildabeast?!?!

  85. Objection! First, cats can swim. Second, if lions are king of the jungle wouldn't the crocs be barred from eating them? Do lions even have predators? Third, the crocs would be downstream to get away from the fire anyway.

  86. I am doing this for school

  87. The solution is to have all planes take off then 3 gives 45 to 1 and 2 after reaching 135. Now with 45 km left 3 heads back. Can you figure out the rest?

  88. Why are there crocodiles if the fire is coming towards the river?

  89. Another Solution
    LL — WWWL
    L — WWWLL
    LLL— WWW
    LL — WWWL
    LLWW- WL
    LW — WWLL
    LWWW- LL
    WWW– LLL
    LLWWW- L
    LWWW– LL
    LLLWWW

    Still 11 tries

  90. Answer:

    Be friends with the crocodiles.

  91. I love how the lions are just waving at the screen

  92. This one was the easiest for me!

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