The first 9 km the bus traveled at a speed of 36 km / h, and the next 27 km at a speed of 54 km / h.

The first 9 km the bus traveled at a speed of 36 km / h, and the next 27 km at a speed of 54 km / h. What is the average speed of the bus?

Travel time when passing 9 km:
t1 = S1 / V1, where S1 = 9 km = 9000 m, V1 = 36 km / h = 36 * 1000/3600 = 10 m / s.
t1 = S1 / V1 = 9000/10 = 900 s.
Travel time when passing 27 km:
t2 = S2 / V2, where S2 = 27 km = 27000 m, V2 = 54 km / h = 54 * 1000/3600 = 15 m / s.
t1 = S1 / V1 = 27000/15 = 1800 s.
Total time:
t = t1 + t2 = 900 + 1800 = 2700 s.
Common path:
S = S1 + S2 = 9000 + 27000 = 36000 m.
Average speed:
V = S / t = 36000/2700 = 13.33 m / s (48 km / h).
Answer. The average bus speed is 13.33 m / s (48 km / h).