Question

A speedboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. What is the speed of the stream in km/hr?

• A. 3.5 km/hr
• B. 4 km/hr
• C. 5 km/hr
• D. 3.25 km/hr

Answer 1

Answer:

C. 5 km/hr

Let the speed of the stream be x km/hr Upstream Speed = 15 + x Downstream Speed = 15 – x {30 / (15+x)} + {30 / (15-x)} = 4 ½ (4 hours 30 minutes) ⇒ {900 / (225-x^2)} = 9/2 ⇒ 9x^2 = 225 ⇒x^2 = 25 ⇒x = 5