Answer:
The Olympic sized swimming pool hold 660501.9 gallons of water.
Step-by-step explanation:
Given that:
Water hold by an Olympic sized swimming pool = 2500000 liters
We know that;
1 gallon = 3.785 liters
Therefore,
We will divide the total number of water in liters by 3.785 to find the number of gallons.
Gallons of water in pool = 
Gallons of water in pool =
gallons
Hence,
The Olympic sized swimming pool hold 660501.9 gallons of water.
In solving this problem we can consider Earth to be a sphere. When we have a circle, then we can use this formula to find arc length:

Where:
L= arc length (in this problem it is disance we need to travel)
R = radius of circle (in this problem it is equal to a radius of Earth)
C = angle we need to pass
We are told that two cities lie halfway around the world. If we fly to west this means angle is 180°.
This gives an arc length of:

If we want to fly to north we need to go to 90° northern latidtude and then back to 17° latitude. This means angle is:
C=2*(90-17)=2*73°=146°
This gives an arc length of:

We can see that flying north is shorter. It is shorter by:
12440.71 miles - 10090.8 miles = 2349.91 miles