#### Answer

Olga had the fastest average speed.

#### Work Step by Step

In order to find average speed, we divide the total distance traveled by the amount of time it took to travel that distance. Thus, we obtain:
Trisha: 10km/2.5hours=4 km per hour
Olga: 9.5km/2.25hours=4.22 km per hour
Jason: 7.5km/2hours=3.75km per hour
Thus, we find that Olga had the fastest average speed.