# Minimum number of persons needed to cross a Desert

In the middle of the confounded desert, there is the lost city of “Ash”.

To reach it, you will have to travel overland by foot from the coast. On a trek like this, *each person can only carry enough rations for five days* and the farthest we can travel in one day is 30 miles. Also, the city is 120 miles from the starting point.

**Answer –** Total 4 persons (including you) required.

**EXPLANATION-**

It is given that each person can only carry enough rations for five days and as there are 4 persons.

Hence, total of 20 days rations is available.

1. **Day 1** : 4 days of rations are used up. One person goes back using one day of rations for the return trip. The rations remaining for the further trek is for 15 days.

2. **Day 2** : The remaining three people use up 3 days of rations. One person goes back using 2 days of rations for the return trip. The rations remaining for the further trek is for 10 days.

3. **Day 3** : The remaining two people use up 2 days of rations. One person goes back using 3 days of rations for the return trip. The rations remaining for the further trek is for 5 days.

4. **Day 4** : The remaining person uses up one day of rations. He stays overnight. The next day he returns to the coast using 4 days of rations.

Thus, total 4 persons, including you are required.

This question is ambiguous: it needs to tell us whether we can leave supplies alone in the desert, or if the supplies must be minded by someone.

If we can leave supplies lying around, then remember that carrying 5 days’ provisions means that starting out, you’ve got enough to travel for 2 days, travel 2 days back, and leave 1 days’ rations on the ground. We also should remember that we only need one person (i.e., ourselves) to make it to Ash, 4 days’ travel away. Lastly, recall that anyone returning to the coast can stock up again and set out again.

So if we think of the midpoint (2 days’ travel) as our refueling stop, and the person going to Ash (me) will need 4 days’ additional supplies to get the further 2 days’ distance and back, then let’s think about this experimentally…

Suppose I take 4 people with me. We start with 5 days’ rations each. After 2 days, they each drop 1 day of rations on the ground (so 4 total), I pick up 2 of them (so I again have 5 total), and then turn around and with their 2 remaining days they hike back to the coast. I take 4 further days to go out to Ash and back to that midpoint. I pick up the last 2 days’ rations on the ground, and finish the journey home alone.

OK, now what if instead they turn around, and come meet me halfway again? Maybe I only need 2 companions. So we start out with 15 rations; 2 days in, we have 9 left. I take 5 of them, leave them with 2 each. They head back to the coast, I continue on to Ash. The night I’m in Ash, they’re back at the coast, stocking up again. The next morning, I leave Ash with 3 (will have 1 at the midpoint), and they set out again with 5 each. We meet 2 days later, I have 1 day of rations left, but they have 3 each and give me 1 apiece, and then we trot back. Okay, that works.

Let’s think about this rationally, though… if I COULD leave supplies alone in the desert, then I wouldn’t need any companions, I could just progressively build up piles of stuff at each day’s waypoint all by myself until I can make the journey given the supplies I’ve left out there. So that doesn’t seem like a fair interpretation of the question. So that’s my answer: **2 companions, 3 of us total**.

Assuming everyone is to be kept alive the answer should be **4.**

**After every day of travel you are left with 4 days ration.
**After 1st day one would return – He would distribute 3 days of ration to remaining others and use 1 to return. So remaining three would be back up to 5.

Similarly after 2nd day one would return distributing two to the others to get them back to 5 and keep 2 for his return.

On 3rd day end another would return giving one to you to get back to 5 and keep 3 for his return.

This five will take you through 5 more days needed to complete the trip.

### Your Answer

## More puzzles to try-

### What is the logic behind these ?

3 + 3 = 3 5 + 4 = 4 1 + 0 = 3 2 + 3 = 4 ...Read More »### Five greedy pirates and gold coin distribution Puzzle

Five puzzleFry ship’s pirates have obtained 100 gold coins and have to divide up the loot. The pirates are all ...Read More »### Defective stack of coins puzzle

There are 10 stacks of 10 coins each. Each coin weights 10 gms. However, one stack of coins is defective ...Read More »### Dr. Willam and surgical gloves puzzle

Dr.Willam wants to operate for three different persons who were wounded. But he had only two surgical gloves. There is ...Read More »### Which clock works best?

Which clock works best? The one that loses a minute a day or the one that doesn’t work at all?Read More »### To which one will the needle touch 1 OR 2

In the gear arrangement, To which one will the needle touch, 1 OR 2Read More »### How did he know?

A man leaves his house in the morning to go to office and kisses his wife. In the evening on ...Read More »### Which letter replaces the question mark

Which letter replaces the question markRead More »### Which room is safest puzzle

A murderer is condemned to death. He has to choose between three rooms. The first is full of raging fires, ...Read More »### (Advanced) Cheryl’s Birthday Puzzle

Paul, Sam and Dean are assigned the task of figuring out two numbers. They get the following information: Both numbers ...Read More »### 2 Eggs and 100 floor Google Classic question

There is a building of 100 floors -If an egg drops from the Nth floor or above it will break. ...Read More »### Probability of having boy

In a country where everyone wants a boy, each family continues having babies till they have a boy. After some ...Read More »### Magical flowers!!

A devotee goes to three temples, temple1, temple2 and temple3 one after the other. In front of each temple, there ...Read More »### How many times a day do all three hands of analog watch overlaps?

There is a perfectly accurate analog watch with hour, minute, and second hands. How many times a day do all three ...Read More »### Tuesday, Thursday what are other two days staring with T?

Four days are there which start with the letter ‘T‘. I can remember only two of them as “Tuesday , Thursday”. ...Read More »### How could only 3 apples left

Two fathers took their sons to a fruit stall. Each man and son bought an apple, But when they returned ...Read More »### How Many Eggs ?

A farmer is taking her eggs to the market in a cart, but she hits a pothole, which knocks over ...Read More »### Most Analytical GOOGLE INTERVIEW Question Revealed

Let it be simple and as direct as possible. Interviewer : Tell me how much time (in days) and money would ...Read More »### Lateral thinking sequence Puzzle

Solve this logic sequence puzzle by the correct digit- 8080 = 6 1357 = 0 2022 = 1 1999 = ...Read More »### Pizza Cost Math Brain Teaser

Jasmine, Thibault, and Noah were having a night out and decided to order a pizza for $10. It turned out ...Read More »