Question

Speed of motorboat in still water is 45kmph. If the motorboat travels 80 km along the stream in 1 hour 20 minutes, then the time taken by it to cover the same distance against the stream will be

• A. 3 hours
• B. 1 hour 20 minutes
• C. 2 hours 40 minutes
• D. 2 hours 55 minutes

Answer 1

Answer:

C. 2 hours 40 minutes

Let the speed of the current be x kmph

Rate downstream = (x + 45) kmph.

According to the question,

$\frac{80}{x+45}=1hours20minutes$

$=\frac{4}{3}$

$4x+180=240$

$4x=240-180$

$x=\frac{60}{4}$

$x=15kmph$

Rate upstream = 45 – 15 = 30 kmph

Required time = $\frac{80}{30}=\frac{8}{3}=2hours40minutes$