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.

Can you solve the river crossing riddle? – Lisa Winer
Tagged on:                                                                                 

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

  • June 24, 2019 at 4:30 am
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    yeah men i like this
    it is hard too

    Reply
  • June 24, 2019 at 3:58 pm
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    Wildebeest and lions can row a raft with their tails?

    um ok then

    Reply
  • June 26, 2019 at 1:15 am
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    This sort of riddle is in poptropica on Nabooti island!!!!!!!

    Reply
  • June 26, 2019 at 5:37 pm
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    Why should I care about the lives of random animals

    Reply
  • June 26, 2019 at 6:21 pm
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    Picasso would be proud of the lions

    Reply
  • June 28, 2019 at 3:13 am
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    why would the animals stay at the left bank instead of just running

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  • June 28, 2019 at 4:24 pm
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    i got it on 7 trips

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  • June 29, 2019 at 11:52 am
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    why can't you just do 2 lions,then 2 wildebeest then 1 lion and 1 wildebeest(together)?

    Reply
  • July 1, 2019 at 7:57 pm
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    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"

    Reply
  • July 3, 2019 at 2:46 am
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    The fire was staying still the whole time

    Reply
  • July 6, 2019 at 4:32 am
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    If i were a wilderbeast or lion, i would just take the boat and make a run for it.

    Reply
  • July 9, 2019 at 12:04 am
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    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

    Reply
  • July 11, 2019 at 8:27 pm
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    Hi sorry but why’s the water green

    Reply
  • July 13, 2019 at 12:06 am
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    This was the video that got me into riddles

    Reply
  • July 14, 2019 at 12:32 pm
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    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!

    Reply
  • July 14, 2019 at 5:34 pm
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    My question is how are the lions and wilder beast so smart. 🤨

    Reply
  • July 15, 2019 at 5:49 am
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    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.

    Reply
  • July 15, 2019 at 1:46 pm
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    Apperantly animals can ride boats 😂

    Reply
  • July 15, 2019 at 7:22 pm
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    Solved it without watching the whole video

    Reply
  • July 18, 2019 at 7:09 pm
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    I actually took the time to solve this and got it right
    My brain got 0.01% bigger today

    Reply
  • July 19, 2019 at 7:16 am
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    0:54 you can just
    Go 2 lions and carrabow at a time and BAM! Problem solved!

    Reply
  • July 20, 2019 at 5:18 am
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    2 wildabeast 2 lions and 1 wildabeast 1 lion

    Reply
  • July 20, 2019 at 11:12 am
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    If ur the buffaloes,ask the lions
    That
    'if I said you to eat me, will you'
    Wait for Yarr or neh

    Reply
  • July 21, 2019 at 4:21 pm
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    These lions cant control their instincts and you expect them to be able to come up with that strategy? Xd

    Reply
  • July 21, 2019 at 9:10 pm
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    Those lions looked so fake🤦🏼‍♂️

    Reply
  • July 21, 2019 at 9:16 pm
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    If it weren't for the lions darn instincts, they could do it in 9 trips😁

    Reply
  • July 22, 2019 at 6:25 pm
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    Finally!!!!!
    after watching tons of riddles I solved one myself!

    Reply
  • July 23, 2019 at 12:08 am
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    Lions and wilderbeest can use rafts, because logic

    Reply
  • July 25, 2019 at 3:35 am
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    Th*t w*s CLEVER!

    Reply
  • July 27, 2019 at 8:05 am
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    Why dont the lions east the wilderbeasts. Less trips!

    Reply
  • July 27, 2019 at 2:27 pm
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    I am happy to solve th problem

    Reply
  • July 28, 2019 at 4:57 am
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    I solved this😎

    Reply
  • July 28, 2019 at 3:47 pm
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    Second riddle solved in 10 minutes. Done

    Reply
  • July 28, 2019 at 10:53 pm
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    I can't believe I actually cracked it

    Reply
  • July 30, 2019 at 1:35 am
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    First time i solve a riddle here.. And that really makes me happy.. Yup..
    High-five needed❤❤😘

    Reply
  • July 30, 2019 at 4:03 am
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    The only one I actually understood

    Reply
  • July 30, 2019 at 11:32 pm
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    animal crossing looks woke

    Reply
  • August 1, 2019 at 11:51 am
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    The man talking was pretty serious and neutral and the animals waving just breaks that and makes me smile

    Reply
  • August 2, 2019 at 8:05 am
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    Just throw the boat across the river…?

    Reply
  • August 4, 2019 at 6:24 pm
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    Solved it myself . Knew this as cannibal and priest riddle

    Reply
  • August 4, 2019 at 6:35 pm
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    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

    Reply
  • August 5, 2019 at 2:52 pm
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    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!

    Reply
  • August 5, 2019 at 3:26 pm
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    Plot twist: the crocodiles just walk out of the water and eat everyone

    Reply
  • August 5, 2019 at 3:26 pm
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    Easier solution: all of the animals squeeze into the raft

    Reply
  • August 7, 2019 at 1:20 am
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    Uhhhh….what?

    Reply
  • August 7, 2019 at 11:25 am
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    If I was the lion, I would go to the other bank and just run

    Reply
  • August 10, 2019 at 5:51 pm
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    That's cool, except the animals dont have time to do all of that

    Reply
  • August 10, 2019 at 6:20 pm
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    Great riddle

    Reply
  • August 11, 2019 at 12:13 am
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    I did this at school

    Reply
  • August 11, 2019 at 12:20 am
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    that was easy

    Reply
  • August 11, 2019 at 2:29 am
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    So what now animal's know how to use rafts, yet

    Reply
  • August 12, 2019 at 4:23 pm
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    3:54 So you’re just gonna tell me that the wildebeest are gonna die anyway???

    Reply
  • August 15, 2019 at 3:27 am
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    Of all the puzzles, this was the only one I solved.

    Reply
  • August 15, 2019 at 9:09 am
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    Wildebeests are f-d anyway.

    Reply
  • August 15, 2019 at 10:44 am
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    You didnt count the chance the 6 crocidle will sink the raft and eat them all

    Reply
  • August 15, 2019 at 2:00 pm
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    they are all participating,so why will the lion will eat the buffalos?

    Reply
  • August 15, 2019 at 3:26 pm
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    A wilderbeest would destroy a lion in a one on one.

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  • August 16, 2019 at 10:43 am
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    you cant save them all, crocodiles and lions need to eat too

    Reply
  • August 17, 2019 at 7:53 am
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    No one is going to mention that the lions' faces have no noses or mouths. The nose and mouth are outside of their manes

    Reply
  • August 17, 2019 at 3:35 pm
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    In reality the lions or wildebeest would just have taken their homies and left the other species to die

    Reply
  • August 18, 2019 at 11:48 am
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    Can’t they just attach a rope to the raft and like just drag it back

    Reply
  • August 18, 2019 at 11:50 am
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    then they realise that a fire is on the other wise of the bank as well and they still die

    Reply
  • August 24, 2019 at 5:43 pm
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    That's were swimming comes in….

    Reply
  • August 24, 2019 at 10:47 pm
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    What if you send 2 lions, then 2 wildebeest, then the last two. It’s all equal and I don’t see any problems.

    Reply
  • August 25, 2019 at 8:45 am
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    OH MY GOD! I ACTUALLY SOLVED TID RIDDLE. I AM SO PROUD OF MYSELF😊

    Reply
  • August 25, 2019 at 6:11 pm
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    Atleast there wasn't a hidden rule or condition that made solution difficult.
    They didn't bend any rules here!

    Reply
  • August 28, 2019 at 8:24 am
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    1 wildabeast 1 lion and 1 wildabeast 1lion and at least the least remaining two

    Reply
  • August 28, 2019 at 4:55 pm
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    Dude . We have to feed the crocodile sometimes .

    Reply
  • August 29, 2019 at 12:08 am
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    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.

    Reply
  • August 30, 2019 at 12:35 pm
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    Boi its ez!
    Put the carabao and lion 2 by 2 and done!

    Reply
  • August 30, 2019 at 5:37 pm
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    If the lion is so friendly with the wilderbeast, that they return to bring them, why would they eat them?

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  • August 30, 2019 at 10:40 pm
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    3 moves.
    1. Beest
    2.Kick back.
    3. Repeat with all animals.

    Reply
  • August 31, 2019 at 2:33 am
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    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~

    Reply
  • August 31, 2019 at 8:02 am
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    I choose…
    All will die becouse they cant paddle a boat
    Im so smart ;D

    Reply
  • August 31, 2019 at 10:24 am
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    Nostalgia! Solved a similar puzzle with 3 priests and 3 devils crossing the river 15 years ago..

    Reply
  • August 31, 2019 at 2:20 pm
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    I did this in no time.
    I liked this

    Reply
  • September 1, 2019 at 12:08 am
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    It’s wildebeest lion the wildebeest lion and wildebeest lion

    Reply
  • September 1, 2019 at 9:37 am
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    ahaha i actually did it

    Reply
  • September 1, 2019 at 10:06 am
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    I have solved it in 9 trips. So the minimum number of trips is 9 not 11. I can challenge that

    Reply
  • September 2, 2019 at 8:42 pm
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    All your need to do is be Jesus and your done

    Reply
  • September 3, 2019 at 10:27 pm
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    I only took 9 steps..how is eleven the shortest amount

    Reply
  • September 4, 2019 at 4:19 am
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    I SOLVED IT!!!!!!!!!

    Reply
  • September 5, 2019 at 8:50 am
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    Just call a swedish minecraft boi, trust me.

    Reply
  • September 6, 2019 at 3:13 pm
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    I DID IT!!!🤓

    Reply
  • September 6, 2019 at 10:02 pm
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    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 .

    Reply
  • September 7, 2019 at 9:06 am
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    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?

    Reply
  • September 8, 2019 at 8:09 am
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    Wait…what's wrong with taking a lion & wildebeast pair across without having to return any on the trip back??…

    Reply
  • September 8, 2019 at 6:25 pm
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    If they're smart enough to use a raft and work together, they're smart enough to not eat

    Reply
  • September 17, 2019 at 12:34 pm
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    3:56 aLIONse

    Reply
  • September 19, 2019 at 11:48 pm
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    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

    Reply
  • September 20, 2019 at 12:19 am
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    There’s a random raft that all animals can move

    Reply
  • September 20, 2019 at 6:00 am
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    I love how the animals just wave all friendly-like even as they're running for their lives from a fire

    Reply
  • September 22, 2019 at 4:50 am
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    1 l W
    2 w w
    3 w w
    4 l l
    5 l l

    Reply
  • September 22, 2019 at 8:11 am
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    Ah yes, a raging fire next to a wooden raft! What could possibly go wrong?

    Reply
  • September 22, 2019 at 2:40 pm
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    No theres a mininum is 4. cause I lion and wilderbeast for 3 times

    Reply
  • September 22, 2019 at 11:53 pm
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    All I know is Runescape helped me solve this problem

    Reply
  • September 29, 2019 at 6:45 pm
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    The least number of crosses is 7 not 11

    Reply
  • October 2, 2019 at 3:08 am
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    Thank you professor Layton for teaching me a similar puzzle to this

    Reply
  • October 3, 2019 at 2:41 am
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    Somehow, I solved it in 9

    Reply
  • October 3, 2019 at 7:57 am
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    Humans: can't solve easy riddles
    Animals: know how to operate a raft and work together

    Reply

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