The speed of a motor-boat is that of the current of water as 36:5. The boat goes along with the current in 5 hours 10 minutes. It will come back in:

15 h 50 min.
26 hours
36 h 50 minutes
412 h 10 minutes

Answer:- 1

Explanation:-

Solution:

Let the speed of the motor boat = 36 kmph and speed of current = 5x kmph. The boat goes along with the current in 5 hours 10 minutes = ³¹/₆ hour;
Hence,

\begin{aligned} Distance \\ = (\frac{31}{6}) \times (36 x + 5 x) \\ = \frac{41 x + 31}{6} k m \\ Speed of boat upstream \\ = 36 x + 5 x = 31 x kmph \\ Hence, time taken to come back \\ = [\frac{(41 x \times (\frac{31}{6}))}{31 x}] \\ = \frac{41}{6} hours \\ = 6 hours 50 minutes \end{aligned}

$\eqalign{ & {\text{Distance}} \cr & = \left( {\frac{{31}}{6}} \right) \times \left( {36x + 5x} \right) \cr & = \frac{{41x + 31}}{6}\,km \cr & {\text{Speed of boat upstream}} \cr & = 36x + 5x = 31x\,{\text{kmph}} \cr & {\text{Hence, time taken to come back}} \cr & = \left[ {\frac{{\left( {41x \times \left( {\frac{{31}}{6}} \right)} \right)}}{{31x}}} \right] \cr & = \frac{{41}}{6}\,{\text{hours}} \cr & = 6\,{\text{hours}}\,50\,{\text{minutes}} \cr}$