The car was moving at a speed of 36 km / h for 20 minutes, and then drove downhill

The car was moving at a speed of 36 km / h for 20 minutes, and then drove downhill at a speed of 72 km / h for 10 minutes, determine the average speed.

Average vehicle speed:
Vav. = S / t, where S is the total distance traveled by the car (S = S1 + S2), t is the total time spent (t = t1 + t2).
The first section of the path:
S1 = V1 * t1, where V1 = 36 km / h, t1 = 20 min or 1/3 h.
Second section of the path:
S2 = V2 * t2, where V2 = 72 km / h, t2 = 10 min or 1/6 h.
Formula:
Vav. = (V1 * t1 + V2 * t2) / (t1 + t2).
Let’s do the calculation:
Vav. = (36 * 1/3 + 72 * 1/6) / (1/3 + 1/6) = 24 / 0.5 = 48 km / h or 13.3 m / s.
Answer: The average vehicle speed was 48 km / h.