[MOVED] Johny wishes to cross the desert, a 7 day trip

G

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Johny wishes to cross the desert, a 7 day trip. Johny and his helpers are able to carry supplies for a maximum of five days.

How many helpers must start out with Johny if he is to cross the desert and his helpers are to either cross with him or return safely to the starting point.
 

arthur ohlsten

Full Member
Joined
Feb 20, 2005
Messages
854
If I understand the problem correctly:

1 Johnny alone could travel 2.5/7 of the trip and return safely, or travel 5/7 th the distance and be stranded,
2 A answer: Let Johnny and 2 friends leave, and at distatance two, each friend gives Johnny provisions for one day, and return with their remaining 2 days provisions. Johny now has 3 day provisions remaining, picks up the 2 day rovisions left by his 2 friends. Johnny has 5 days provisions to travel the remaining 5 day trip.
 

Denis

Senior Member
Joined
Feb 17, 2004
Messages
1,459
Agree Arthur; and the 2 helpers need only 4 days supplies:

j = johnny, a = helper, b = helper

After 1 day: j = 4, a = 3, b = 3; b gives j and a 1 day each;
b returns with the 1 day he has left; now j = 5 and a = 4

After 2 days: j = 4, a = 3; a gives j 1 day;
a returns with the 2 days he has left; now j = 5 : enough to finish
 
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