# Half of the time the car is moving at 30 km / h, the remaining half at 70 km / h. Determine the average speed of the car.

V1 = 30 km / h.

V2 = 60 km / h.

t1 = t2 = t / 2.

Vav -?

To find the average vehicle speed Vav, it is necessary to divide the entire path S it has traveled by the time of its movement t: Vav = S / t.

The entire traversed path will be the sum: S = S1 + S2, where S1 is the path of the first part of the path, S2 is the path of the second part of the path.

S1 = V1 * t1 = V1 * t / 2.

S2 = V2 * t2 = V2 * t / 2.

S = V1 * t / 2 + V2 * t / 2 = (V1 + V2) * t / 2.

Vav “= (V1 + V2) * t / 2 * t = (V1 + V2) / 2.

Vav “= (30 km / h + 60 km / h) / 2 = 45 km / h.

Answer: the average speed of the vehicle was Vav = 45 km / h.

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