For half an hour, the boy rode a bicycle at a speed of 24 km / h and then walked 6 km at a speed of 4 km / h

For half an hour, the boy rode a bicycle at a speed of 24 km / h and then walked 6 km at a speed of 4 km / h. Determine the average speed of movement

Boy’s average speed:
Vav. = S / t, where S is the total distance covered (S = S1 + S2, where S2 = 6 km), t is the total travel time (t = t1 + t2, where t1 = 0.5 h).
Track section S1:
S1 = V1 * t1, where V1 = 24 km / h
Travel time when passing the section of the path S1:
t2 = S2 / V2, where V2 = 4 km / h.
Let’s calculate the average speed of the boy:
Vav. = (S1 + S2) / (t1 + t2) = (V1 * t1 + S2) / (t1 + S2 / V2) = (24 * 0.5 + 6) / (0.5 + 6/4) = 18 / 2 = 9 km / h.
Answer: The average speed of the boy is 9 km / h.