With what average speed did the body move, if the part of the path is equal to 108 km

With what average speed did the body move, if the part of the path is equal to 108 km, it passed in 36 km / h. a part equal to 108 km at a speed of 54 km / h, and a part equal to 72 km for 72 km / h?

V1 = 36 km / h.

S1 = 108 km.

V2 = 54 km / h.

S2 = 108 km.

V3 = 72 km / h.

S3 = 72 km.

Vav -?

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

The travel time of the entire path is expressed by the sum: t = t1 + t2 + t3, where t1, t2, t3 are the travel time on the first, second and third part of the path.

t1 = S1 / V1.

t1 = 108 km / 36 km / h = 3 h.

t2 = S2 / V2.

t2 = 108 km / 54 km / h = 2 h.

t3 = S3 / V3.

t3 = 72 km / 72 km / h = 1 h.

t = 3 h + 2 h + 1 h = 6 h.

S = S1 + S2 + S3.

S = 108 km + 108 km + 72 km = 288 km.

Vav = 288 km / 6 h = 48 km / h.

Answer: the average body speed was Vav = 48 km / h.