Cross the desert | 27 Aug 2009

shabbir's Avatar, Join Date: Jul 2004
Go4Expert Founder
Man has to cross a barren desert that requires 6 days to cross. One man can carry food for max of 4 days. What is the fewest number of other men required to help carry enough food for you to cross?
anju.hifi's Avatar
Go4Expert Member
each person needs 6 days of food
There is 1 white man and X coolies
Each coolies can only carry 4 days of Food
6 * (1 + X) = 4 * X
6 + 6 X = 4 X
6 + 2 X = 0
3 + X = 0
X = -3
ANSWER He need -3 coolies to cross the desert,
nimesh's Avatar, Join Date: Apr 2009
Invasive contributor
what kind of calculation was that?
nimesh's Avatar, Join Date: Apr 2009
Invasive contributor
There are probably a lot of ways to solve this but my way was first to realize that if each of the men ate his own food then even if we begin with a hundred men, each can only get four days into the desert. Clearly the idea is to get only the one explorer across and have the helpers return back. By simply trying a few ideas the answer is clearly that two other men are required.

The first helper only goes on day into the desert. He feeds the other two men during the first day, so that at the beginning of the second day, he only has one day rations left. So he goes back to camp. On the second day, the second helper feeds himself and the explorer. On the beginning of the third day the helper now has two days rations left so he heads back. The explorer is two days into the journey and still has all four days of his food left, so he continues on alone.

Three men, each with 4-days of food head out (day 1).
The next day eachhas three days worth of food.

The first man gives one-days rations to each of the other 2. That leaves him with one day's rations to go back.

The other two, now with 4-days of rations continue (day 2)

The next day the second man gives one-days worth of rations to the third man. The second man has 2-days of rations to go back. The third man now has 4-days of rations to make the 4-day trip across the desert.

Day 1 - 3 Persons - 3*4 = 12
Day 2 - 3 Persons - 3*3 = 9
one man leaves and takes food for his return
Day 2 - 2 Persons - 3*3 - 1 = 8
Day 3 - 2 Persons - 8 - 2 = 6
Second man leaves and takes food for his return
Day 3 - 1 Persons - 6 - 2 = 4 which is enough for the third man to complete his 4 day journey
kiddo's Avatar
the question is confusing me....
But my assumption answer is '1'.

reason :
in my point of view this question is,
me as man who want to cross the dessert that can carry food max for 4 days.
I need men to help me, and each of them can carry food for the same term.
so we can make the function like this.
6x - 4x = 0

which means 6x -> food needed
and 4x -> food can be carried
for x=1, 2=0
for x=2, 4=0
for x=3, 6=0
for x=n, 2^n=0

so I think the closest answer is x=1,
that man the fewest other men is just 1.

Is this assumption right?
or just my assumption is nonsense?
kiddo's Avatar
I know the answer..
the answer is 3, right?
kiddo's Avatar
a = me
b,c = other men

Day 1 : a(4),b(4),c(1)
Day 2 : a(4),b(2)
Day 3 : a(3)
Day 4 : a(2)
Day 5 : a(1)
Day 6 : arrive

*b & c go back

if me isn't included as other man,
the answer is 2.
shabbir's Avatar, Join Date: Jul 2004
Go4Expert Founder
Congrats nimesh
nimesh like this
mayjune's Avatar, Join Date: Jun 2009
Invasive contributor
Nimesh aka KFP
Hehehe I like that