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        riddles >> easy >> River Crossing (I)
        
(Message started by: THUDandBLUNDER on Jun 1^st, 2003, 4:05am)

Title: River Crossing (I)
Post by THUDandBLUNDER on Jun 1^st, 2003, 4:05am

Three soldiers have to cross a river without a bridge. Two boys with a boat agree to help the soldiers, but the boat is so small it can support only one soldier or two boys. A soldier and a boy can't be in the boat at the same time for fear of sinking it. Given that none of the soldiers can swim, it would seem that in these circumstances just one soldier could cross the river. Yet all three soldiers eventually end up on the other bank and return the boat to the boys. How do they do it?

Title: Re: River Crossing (I)
Post by WombatDeath on Jun 1^st, 2003, 6:01am

Are [hide] the boys allowed to swim [/hide] ?

Failing that:
[hide]
Boy 1 is dropped off on the far bank.
Boy 2 rows back.
Soldier 1 rows to the far side.
Boy 1 rows to the near side.
Boy 2 gets in, and both row to the far side.
Return to step 1, and repeat for the other soldiers.
[/hide]

Title: Re: River Crossing (I)
Post by THUDandBLUNDER on Jun 1^st, 2003, 6:27am

Quote:

Are the boys allowed to swim ?

Nyet.

Title: Re: River Crossing (I)
Post by TenaliRaman on Jun 1^st, 2003, 7:02am

Let us call the boys as B1 and B2,
the soldiers as S1,S2 and S3,
and the banks as bank1 and bank2.

Situation :
At bank1 : B1,B2,S1,S2,S3
At bank2 : nobody

1>Boys B1 and B2 go from bank1 to bank2.Boy B2 is dropped off at bank2 and boy B1 returns.

Situation :
At bank1 : B1,S1,S2,S3
At bank2 : B2

2>Soldiers S1 takes the boat and goes to bank2.From there boy B2 takes the boat and comes to bank1.

Situation :
At bank1 : B1,B2,S2,S3
At bank2 : S1

3> Repeat Step 1.

Situation :
At bank1 : B1,S2,S3
At bank2 : S1,B2

3>Soldiers S2 takes the boat and goes to bank2.From there boy B2 takes the boat and comes to bank1.

Situation :
At bank1 : B1,B2,S3
At bank2 : S1,S2

4>Repeat Step 1.

Situation :
At bank1 : B1,S3
At bank2 : S1,S2,B2

5>Soldiers S3 takes the boat and goes to bank2.From there boy B2 takes the boat and comes to bank1.

Situation :
At bank1 : B1,B2
At bank2 : S1,S2,S3

This is the answer unless i have made any mistake in understanding the question.

Title: Re: River Crossing (I)
Post by Chronos on Jun 1^st, 2003, 1:50pm

As a matter of fact, the boys can use the same method to ferry any number of soldiers across, although it may take a while.