From one city to another, the car drove 3 with 20 minutes. One tenth of the total driving time

From one city to another, the car drove 3 with 20 minutes. One tenth of the total driving time, he was driving at a speed of 90 km / h, and the rest of the time – at a speed of 60 km / h. What distance did the car travel? What is the average speed of a car along the way?

Given:
t = 3 hours 20 minutes = 12000 seconds – total travel time;

v1 = 90 km / h = 25 m / s – speed of movement within 0.1 * t time;

v2 = 60 km / h = 16.7 m / s – movement speed during 0.9 * t time.

It is required to determine the distance traveled by the car S (meters) and the average speed vav (m / s).

The total distance traveled by the car is equal to:

S = S1 + S2 = v1 * 0.1 * t + v2 * 0.9 * t = 25 * 12000 * 0.1 + 16.7 * 12000 * 0.9 = 30000 + 180360 = 210360 meters.

Then the average speed will be equal to:

vav = S / t = 210360/12000 = 17.5 m / s.

Answer: the total distance covered is 210,360 meters (210.4 kilometers), the average speed is 17.5 m / s (63 km / h).