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# Humans and Monkeys

## 38 posts in this topic

Humans and Monkeys - Back to the River Crossing Puzzles

Three humans, one big monkey and two small monkeys are to cross a river:

* Only humans and the big monkey can row the boat.

* At all times, the number of humans on either side of the river must be greater or equal to the number of monkeys on that side. (Or else the humans will be eaten by the monkeys!)

* The boat only has room for 2 (monkeys or humans).

* Monkeys can jump out of the boat when it's banked.

This old topic is locked since it was answered many times. You can check solution in the Spoiler below.

Pls visit New Puzzles section to see always fresh brain teasers.

Humans and Monkeys - solution

The three columns represent the left bank, the boat, and the right bank respectively. The < or > indicates the direction of motion of the boat.

HHHMmm . .

HHHm Mm> .

HHHm <M m

HHH Mm> m

HHH <M mm

HM HH> mm

HM <Hm Hm

Hm HM> Hm

Hm <Hm HM

mm HH> HM

mm <M HHH

m Mm> HHH

m <M HHHm

. Mm> HHHm

. . HHHMmm

HUH!?!?

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. is an empty bank (or an empty boat in the first and the last step)

H is a human

M is a big monkey

m is a small monkey

> is going right

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ok, nevermind, I didn't understand the monkeys jump out when it banks at first....

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ADMIN this is yours 15 steps (and this is mine 12 steps)

The three columns represent the left bank,

the boat, and the right bank respectively.

The < or > indicates the direction of motion of the boat.

HHHMmm . . (HHHMmm . .)

HHHm Mm> . (HHHm Mm> .)

HHHm

HHH Mm> m (HHH Mm> m)

HHH

HM HH> mm (HM HH> mm)

HM

Hm HM> Hm ---------

Hm Hm)

mm HH> HM (Mm

mm HHm)

m Mm> HHH (M

m HHHMmm)

. Mm> HHHm

. . HHHMmm

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ADMIN this is yours 15 steps (and this is mine 12 steps)

The three columns represent the left bank,

the boat, and the right bank respectively.

The < or > indicates the direction of motion of the boat.

HHHMmm . . (HHHMmm . .)

HHHm Mm> . (HHHm Mm> .)

HHHm

HHH Mm> m (HHH Mm> m)

HHH

HM HH> mm (HM HH> mm)

HM

Hm HM> Hm ---------

Hm Hm)

mm HH> HM (Mm

mm HHm)

m Mm> HHH (M

m HHHMmm)

. Mm> HHHm

. . HHHMmm

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if the number of humans is zero on one side but there are multiple monkeys does it matter? (after all, the humans cannot be eaten if they are not there)

HHHMmm...

HHMm >Hm...

HHMm...Hm

HM >Hm...Hm

HM...HHmm

>HM...HHmm

...HHHMmm

sounds rite ???

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HHH, Mmm

HH mm HM> ........

HH mm <M H

HH m Mm> H

HH m <H Mm

HH Hm> Mm

HH <H Mmm

H HH> Mmm

H <M HH mm

........ HM> HHH Mmm

........ ...... HHH Mmm

Isn't this right

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Actually, if you properly adhere to the puzzle requirements there is no apparent solution. Even the admin's solution violates the requirement "At all times, the number of humans on either side of the river must be greater or equal to the number of monkeys on that side". At any time, any side having only monkeys violates this rule since 0 Humans is not greater or equal to 1, 2 or 3 monkeys.

For the admin solution to be correct, the requirement would need to be revised to state "At all times, the number of humans must be greater or equal to the number of monkeys on any side of the river having both monkeys and humans".

HHHMmm . .

HHHm Mm> . <<< Right Side has 2 Monkeys and 0 Humans

HHHm

HHH Mm> m <<< Right Side has 3 Monkeys and 0 Humans (once banked)

HHH

HM HH> mm

HM

Hm HM> Hm

Hm

mm HH> HM <<< Left Side has 2 Monkeys and 0 Humans

mm

m Mm> HHH <<< Left Side has 1 Monkey and 0 Humans

m

. Mm> HHHm

. . HHHMmm

Some would say having only monkeys on a given side would not result in a human being eaten by monkeys. That may sound reasonable, but the rule still exists that # Humans >= Monkeys "At all times ... on either side".

Chris

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Big Monkey always rows the boat. First take a human, then a monkey, then Human, then monkey, then human.

HHHmmM ---------

HHmm MH >

HHmm

HHm Mm > H

HHm < M Hm

Hm MH > Hm

Hm < M HHm

H Mm > HHm

H < M HHmm

MH > HHmm

HHHMmm

There are always the same or more humans on each side. However,

BIG MONKEY worked up an appetite taking everyone across the river and ate all the humans and the monkeys. Haven't you seen King Kong? OOGA BOOGA

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Big Monkey always rows the boat. First take a human, then a monkey, then Human, then monkey, then human.

HHHmmM ---------

HHmm MH >

HHmm

HHm Mm > H <--- There are 3 monkeys and 2 humans before the boat sets out.

HHm < M Hm

Hm MH > Hm

Hm < M HHm

H Mm > HHm

H < M HHmm <--- There are 3 monkeys and 2 humans before the boat sets out.

MH > HHmm

HHHMmm

There are always the same or more humans on each side. However,

BIG MONKEY worked up an appetite taking everyone across the river and ate all the humans and the monkeys. Haven't you seen King Kong? OOGA BOOGA

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have the big monkey go back and forth in the boat, and ferry every1 over 1 by one when alternating starting with a human

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"Ankur" Remember that some one has to send the boat back

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O=big monkey

m=little monkey

X=human

>=across the bank

<=back from across the bank

XX>

X<

XX>

X<

Xm>

X<

Xm>

X<

XO>

im the best in the world

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O=big monkey

m=little monkey

X=human

>=across the bank

<=back from across the bank

XX>

X<

XX>

X<

Xm>

X<

Xm>

X<

XO>

im the best in the world

In your very first line, you have already left 1 human (X) behind with all of the monkeys (m & O). You have to consider the number of monkeys and humans on both sides.

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I don't see how any of these solutions work due to this line:

* At all times, the number of humans on either side of the river must be greater or equal to the number of monkeys on that side. (Or else the humans will be eaten by the monkeys!)

If it clarified that it's okay for a monkey to be alone I could understand, but it doesn't clarify that. It says AT ALL TIMES - GREATER OR EQUAL TO. Basically that's a trap. If this were true this would be impossible to solve.

This is not a smart or good puzzle in my opinion.

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Humans and Monkeys...

his is wrong because a man and a small monkey CANNOT! ride together, though ilogical that a big monkey is less threating or is easy to go across a river with than a small monkey it is the rule. no my way seem to be way easier and follows the rules

HHHMmm . . HHHMmm. .

HHHm Mm>. HHmm HM>..

HHHm <M m HHmm <M H

HHH Mm> m HHm Mm> H

HHH <M mm HHm <M Hm

HM HH> mm Hm MH> HHm

HM <Hm Hm Hm <M HHm

Hm HM> Hm m HM> HHm

Hm <Hm HM m <M HHHm

mm HH> HM .. mM> HHHm

mm <M HHH ... HHHMmm

m Mm> HHH

m <M HHHm

. Mm> HHHm

..HHHMmm

try to correct because i see no flaw <!-- s8) --><!-- s8) -->

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Humans and Monkeys...

his is wrong because a man and a small monkey CANNOT! ride together, though ilogical that a big monkey is less threating or is easy to go across a river with than a small monkey it is the rule. no my way seem to be way easier and follows the rules

HHHMmm . . HHHMmm. .

HHHm Mm>. HHmm HM>..

HHHm <M m HHmm <M H

HHH Mm> m HHm Mm> H

HHH <M mm HHm <M Hm

HM HH> mm Hm MH> HHm

HM <Hm Hm Hm <M HHm

Hm HM> Hm m HM> HHm

Hm <Hm HM m <M HHHm

mm HH> HM .. mM> HHHm

mm <M HHH ... HHHMmm

m Mm> HHH

m <M HHHm

. Mm> HHHm

..HHHMmm

try to correct because i see no flaw <!-- s8) --><!-- s8) -->

I am right because a human and a small monkey CAN! ride together ... where does it say the opposite?

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I think that one big monkey, two small monkeys, and two humans initially approach a boat when they initiate this endeavor. Wouldn't that immediately put a stop to this problem since, before any thing gets on the boat the first time we're already dealing with a situation where we have 3 monkeys and 2 humans?

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Another solution that requires the same 13 crossings is:

HHHMmm...

HHMm Hm>

HHMm

HHH Mm> m

HHH

HM HH> mm

HM

Hm HM> Hm

Hm

mm HH> HM

mm

m Mm> HHH

m

mM> mHHH

...mmMHHH

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Only big monkey and humans can row the boat and # of human has to be >= # of monkeys

HHHMmm

HHHm --> Mm

HHHm <-- M m

HHm --> MH m

HHm <-- M Hm <----- being eaten

Hm --> MH Hm

Hm <-- M HHm <----- being eaten

H --> Mm HHm <----- being eaten

H <-- M HHmm

--> MH HHmm

HHHMmm

I totally forgot the the last point where the monkey can jump out of the boat.

So it will have to be revised according to the solution.

Edited by biodreamer

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what with all the h's and m's and >'s and <'s and .'s i just have one thing to say:

Hmmmmm>Hmmmmm<Hmmmm....???

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HHHMmm...

HHMm >Hm...

HHMm...Hm

HM >Hm...Hm <---who will bring back the boat

HM...HHmm

>HM...HHmm

...HHHMmm

sounds rite ???