The bus moved for 2 hours at a speed of 15 m / s, and then another 12 km at a speed of 20 m / s.

The bus moved for 2 hours at a speed of 15 m / s, and then another 12 km at a speed of 20 m / s. What is its average speed all the way?

Average travel speed:
Vav. = S / t, where S is the total route covered by the bus (S = S1 + S2, where S2 = 12 km = 12000 m), t is the total travel time (t = t1 + t2, where t1 = 2 h = 2 * 3600 = 7200 s).
S1 = V1 * t1, where V1 = 15 m / s.
t2 = S2 / V2, where V2 = 20 m / s.
Vav. = (S1 + S2) / (t1 + t2) = (V1 * t1 + S2) / (t1 + S2 / V2) = (15 * 7200 + 12000) / (7200 + 12000/20) = 120000/7800 = 15 , 38 m / s (55.38 km / h).
Answer: The average speed of the bus is 15.38 m / s (55.38 km / h).