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.

100 thoughts on “Can you solve the river crossing riddle? – Lisa Winer

  1. You wasted a lot of time. Just send two of each then do the last step!

  2. Here’s my solution I know it doesn’t make sense for them but here’s how it goes first send out two wildebeest then send out two lions then send out One of each and it’s done

  3. I did it. Just got confused when I had to put 2 animals to go back on one turn

  4. why can't you just do 2 lions,then 2 wildebeest then 1 lion and 1 wildebeest(together)?

  5. How do animals have the ability to control a raft, how do animals know this complicated solution, and Isn't the fire going to reach them according to the vid it says "as a wildfire rages through the grasslands"

  6. If i were a wilderbeast or lion, i would just take the boat and make a run for it.

  7. This is my Solution

    Two lions cross the river ,they push the raft too the other side, and run away, two wilderbeasts cross the river, they push the raft too the other side, and run away one wilderbeast and one lion cross the river, and run away

  8. This was the video that got me into riddles

  9. 0:50
    Ted ed ( or Teddy Eddie as I like to call it ) – What's the fastest way for all six animals to get across?
    Me – why does it matter to me what's gonna happen to these animals? Now THATS a riddle to talk about!

  10. My question is how are the lions and wilder beast so smart. 🤨

  11. 1:50 when the lion gets back, just shove him on the beach and take the two wilder beasts. Then you’re done after you take the lions.

  12. I actually took the time to solve this and got it right
    My brain got 0.01% bigger today

  13. 0:54 you can just
    Go 2 lions and carrabow at a time and BAM! Problem solved!

  14. If ur the buffaloes,ask the lions
    That
    'if I said you to eat me, will you'
    Wait for Yarr or neh

  15. These lions cant control their instincts and you expect them to be able to come up with that strategy? Xd

  16. If it weren't for the lions darn instincts, they could do it in 9 trips😁

  17. First time i solve a riddle here.. And that really makes me happy.. Yup..
    High-five needed❤❤😘

  18. The man talking was pretty serious and neutral and the animals waving just breaks that and makes me smile

  19. There are three river crossing riddles that are difficult, 4 couples crossing wherein cross coupling is forbidden: two mothers with twins and a police with favour wherein the children can travel only with their mother or police, and the most complicated one a farmer with two cabbage, two goat, two bulls and one wolf.
    I solved the first two but till now not able to solve the last one

  20. If the lions are sensible enough to not eat the wildebeest while they’re on the raft, why not just…don’t? Just don’t eat them at all? Or better yet, just jump on the crocodiles!
    Come on, guys! Use some common sense!

  21. Plot twist: the crocodiles just walk out of the water and eat everyone

  22. 3:54 So you’re just gonna tell me that the wildebeest are gonna die anyway???

  23. You didnt count the chance the 6 crocidle will sink the raft and eat them all

  24. they are all participating,so why will the lion will eat the buffalos?

  25. No one is going to mention that the lions' faces have no noses or mouths. The nose and mouth are outside of their manes

  26. In reality the lions or wildebeest would just have taken their homies and left the other species to die

  27. Can’t they just attach a rope to the raft and like just drag it back

  28. then they realise that a fire is on the other wise of the bank as well and they still die

  29. What if you send 2 lions, then 2 wildebeest, then the last two. It’s all equal and I don’t see any problems.

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

  31. 1 wildabeast 1 lion and 1 wildabeast 1lion and at least the least remaining two

  32. Wouldn’t the fire have already reached them? If they were running to the river it would’ve taken them at least 10 mins for them all to get across + rivers can be very wide.

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

  34. 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~

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

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

  37. 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 .

  38. 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?

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

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

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