Question:

There are 3 men, two Chimps, and one Gorilla on one side of a river:

• They have a boat but only the men and the Gorilla can row the boat across, so there must always be a human and/or Gorilla on the boat.
• The boat can only carry two people/monkeys.
• If monkeys and humans are together on one side of the river there must be as many or more people than monkeys for the men’s safety.
How can all men and monkeys make it to the other side?

.

.

C

A

P

T

A

I

N

I

N

T

E

R

V

I

E

W

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Solution: Steps: (They all start on the left side).

(Left side | Right side)

(3 men, 1 Gorilla, 2 Chimps | 0 men, 0 Gorilla, 0 Chimps)
-> Chimp and Gorilla (3 men, 0 Gorilla, 1 Chimps | 0 men, 1 Gorilla, 1 Chimps)
<- Gorilla (3 men, 1 Gorilla, 1 Chimps | 0 men, 0 Gorilla, 1 Chimps)
-> Chimp and Gorilla (3 men, 0 Gorilla, 0 Chimps | 0 men, 1 Gorilla, 2 Chimps)
<- Gorilla (3 men, 1 Gorilla, 0 Chimps | 0 men, 0 Gorilla, 2 Chimps)
-> Two men (1 men, 1 Gorilla, 0 Chimps | 2 men, 0 Gorilla, 2 Chimps)
<- Human and Chimp (2 men, 1 Gorilla, 1 Chimps | 1 men, 0 Gorilla, 1 Chimps)
-> Human and Gorilla (1 men, 0 Gorilla, 1 Chimps | 2 men, 1 Gorilla, 1 Chimps)
<- Human and Chimp (2 men, 0 Gorilla, 2 Chimps | 1 men, 1 Gorilla, 0 Chimps)
-> 2 men (0 men, 0 Gorilla, 2 Chimps | 3 men, 1 Gorilla, 0 Chimps)
<- Gorilla (0 men, 1 Gorilla, 2 Chimps | 3 men, 0 Gorilla, 0 Chimps)
-> Gorilla and Chimp (0 men, 0 Gorilla, 1 Chimps | 3 men, 1 Gorilla, 1 Chimps)
<- Gorilla (0 men, 1 Gorilla, 1 Chimps | 3 men, 0 Gorilla, 1 Chimps)
-> Gorilla and Chimp (0 men, 0 Gorilla, 0 Chimps | 3 men, 1 Gorilla, 2 Chimps)

And they are all safely across.