**First read T&Cs of the journey! **
Let's assume that the only airport mentioned is located at the **top **of the earth.
Recollect all the data given.
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**1. **The professor's plane must make a** single continuous** trip around the world without landing or turning around.
2. Each plane can travel exactly** 1 degree of longitude** in **1 minute**
for every kiloliter of fuel. Each can hold a maximum of 180 kiloliters
of fuel.
3. Any plane can refuel any of the others in mid-air by meeting at the same point and instantly transferring any amount of fuel.
4. **Fugari** and** Orokana's** planes can turn around instantaneously without burning fuel.
5. Only **one** airport is available for any of the planes to land, take off, or refuel.
6. All three planes must** survive** the experiment, and none may run of fuel in mid-air.
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As per (2), since each plane travel** 1 degree of longitude in 1 minute** for every** kiloliter** of fuel, means that plane need **360 minutes **(6 hours) and **360 kiloliters **of fuel. But remember plane can hold only 180 kiloliters
of fuel.
Let's suppose that, all three planes takes off from airport exactly at 12:00 PM towards the **WEST.**
We will break this 6 hours journey into 8 parts where each plane travels 45 degree of longitude east or west using 45 kiloliters of fuel.
**START :**
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PART 1 :

Exactly at **12:45 PM**, all will be at** 45** degree angle with reference to the center of the earth.
At this point, each of them will use **45** kiloliters of fuel. Hence, each will have **135** kiloliters of fuel. Here, **Orokana** gives away **45** kiloliters to each of **Fukano** & **Fuga****ri.** So she is left with the **45** kiloliters which she uses to go back to the starting point.
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**PART 2 : **

**In** next 45 minutes, both **Fukano** and **Fugari** moves to **90 **degree of longitude spending **45** kiloliters of fuel. Now,here both will have **135** kiloliters each in their fuel tank. Here, **Fugari** refuels** Fukano's** fuel tank with **45** kiloliters of fuel; leaving **90** kiloliters in own tank for the backward journey towards the starting point.

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**PART 3 : **
**Fukano** travels further, while** Fugari** is in midway of the backward journey. Again, both spend** 45** kiloliters of fuel.

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**PART 4 :**

Exactly at **3:00 PM**, **Fukano** reaches at **180** degree while** Fugari** reaches back to the **starting point.** Till then,** Orokana** refuels her plane & takes off towards **EAST.** She has to take off as **Fukano **is left with only** 90 kiloliters** of fuel by which he could travel** half** of the rest of journey.

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**PART 5 :**

In next** 45** minutes,** Fukano's **plane uses 45 kiloliters further while **Orokana** travels** 1/3rd** of **Fukano's** remaining journey in **reverse** direction so as to meet **Fukano** in midway. In process, her plane again uses** 45** kiloliters of fuel with **135** kiloliters left.

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**PART 6 :**

At **04:30 PM**, **Orokana** meets **Fukano** whose plane had no fuel left at the point & refuels his plane with 45 kiloliters of fuel.** **Remember **Orokana's** plane consumed 45 kiloliters more till she meets** Fukano**. Now, since both of them have left only **45** kiloliters in fuel tank, **Fugari** whose plane standing at airport is refueled at full **180** kiloliters takes of in the direction of **EAST.**

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**PART 7 : **

At** 05:15 PM**, when fuel tank indicators of both Fukano & Orokana are pointing to **0**, Fugari meets them & gives** 45** (to Fukano) +** 45** (to Orokana) = **90** out of **135** (180 - 45 used since take off) . Now all are left with **45** kiloliters of fuel &** 45** degrees of journey is left.

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**PART 8 : **
And this is how, exactly at** 06:00 PM** all of them reaches back to the starting point **safely.**
But is this the most efficient way to make trip around the Earth? Certainly not!
If plane was built with fuel tank of 360 + then the mission wouldn't have required any assistance. Just because of limited fuel tank, 45 + 45 + 90 + 90 + 90 + 90 + 45 + 45 = 270 Kiloliters of fuel burnt to assist Fukano's plane.
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