Question

The speed of a boat in still water is 15 km/hr. It can go 30 km upstream and return downstream to the original point in 4 hrs 30 min. The speed of the stream is:

• A. 12 km/hr
• B. 8 km/hr
• C. 5 km/hr
• D. 10 km/hr

Answer 1

Answer:

C. 5 km/hr

Explanation: 

D $=t [\frac{(u2-v2)}{2u}] 30$

$= (4\frac{1}{2})\times{[\frac{(152-v2)}{2\times{15}}]}$

$= \frac{9}{2}[\frac{(225-v2)}{30}]$

200=225- v2

v2=25

v=5km/hr.