The boy ran 600m to the store in 4 minutes. Made a purchase in 8 minutes.

The boy ran 600m to the store in 4 minutes. Made a purchase in 8 minutes. How long did the boy spend in the store if his average speed is 3.6 km / h.

Task data: S1 (distance that the boy ran to the store) = 600 m; t1 (duration of movement to the store) = 8 minutes (480 s); Vav. (boy’s average speed) = 3.6 km / h (1 m / s).

We express the time the boy spent in the store from the formula: Vav. = (S1 + S2) / (t1 + t2) = (S1 + 0) / (t1 + t2), whence t2 = S1 / Vav. – t1.

Calculation: t2 = 600/1 – 480 = 120 s (2 min).

Answer: The boy spent 2 minutes in the store.