# The train traveled 1 half of the way at a speed of 72 km / h, the second half of the way at a speed of 36 km / h,

The train traveled 1 half of the way at a speed of 72 km / h, the second half of the way at a speed of 36 km / h, determine the average speed of the train along the entire route.

Average speed = All the way: All the time.

Let S be the entire distance.

The first half of the journey is S / 2 km, this section of the route the train was traveling at a speed of 72 km / h, we calculate the travel time:

t1 = S / 2: 72 = S / 144 (h).

The second half of the journey is also equal to S / 2 km, this section of the route the train traveled at a speed of 36 km / h, we calculate the travel time:

t2 = S / 2: 36 = S / 72 (h).

Hence, all the time is equal to t = t1 + t2.

Let’s express the average speed:

vav = S / t = S / (S / 144 + S / 72) = S / (3S / 144) = 144S: 3S = 144: 3 = 48 (km / h).

Answer: the average speed is 48 km / h.

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