The car traveled three quarters of its way at 60 km / h, and the rest of the way at 80 km / h.

The car traveled three quarters of its way at 60 km / h, and the rest of the way at 80 km / h. What is the average vehicle speed?

Average travel speed:
Vav. = S / t, where S is the total distance traveled (S = S1 + S2, where S1 = 3/4 S, S2 = 1/4 S), t is the total travel time (t = t1 + t2).
S1 = V1 * t1, S2 = V2 * t2, V1 = 60 m / s, V2 = 80 m / s.
Travel time when passing S1, S2:
t1 = S1 / V1 = (3 / 4S) / 60; t2 = S2 / V2 = (1 / 4S) / 80.
Let’s calculate the average speed:
Vav. = S / t = S / ((3 / 4S) / 60 + (1 / 4S) / 80) = S / (0.0125S + 0.003125S) = 1 / 0.015625 = 64 km / h.
Answer: The average speed is 64 km / h.