2015 · Q26
A motor boat, whose speed is 15 km/hour in still water goes 30 km downstream and comes back in a total of 4 hour and 30 minutes. The speed of the stream is
Elementary MathematicsRatio and Proportion
- A4 km/hour
- B5 km/hour
- C6 km/hour
- D10 km/hour
Explanation
30/(15 + v) + 30/(15 - v) = 4.5 gives 900/(225 - v^2) = 4.5, so v^2 = 25 and v = 5 km/h. Hence option (b).