Final answer:
The magnitude of the total displacement of Olivia's trip is 2 miles.
Step-by-step explanation:
The total displacement of Olivia's trip can be found by adding up the individual displacements along each direction. Olivia rides 0.9 mi south, 0.8 mi east, and 1.2 mi east. Since the north-south displacement cancels out, the total east-west displacement is 0.8 mi + 1.2 mi = 2 miles. Therefore, the magnitude of the total displacement of her trip is 2 miles.