A motorboat travelling at 15 km/hr on calm water travels 30 km downstream and returns in 4 hours 30 minutes. The stream's speed (in kilometres per hour) is:
A. 4
B. 5
C. 6
D. 10
Answer:B
A motorboat travelling at 15 km/hr on calm water travels 30 km downstream and returns in 4 hours 30 minutes. The stream's speed (in kilometres per hour) is:
A. 4 B. 5 C. 6 D. 10
Explanation: Let's say the stream's speed is x km/hr. Then,Downstream speed = (15 + x) km/hr,Upstream speed = (15 - x) km/hr,4 1/2 = 30/(15 + x) + 30/(15 - x),9/2 = 900/225 - x2,225 = 9x2,25 x2 =x equals 5 km/hr.