Question

The ratio of speeds of a motor boat to that of the current of water is $36:5$. The motor boat goes along with the current is $5$ hr $10$ min. Find the time to come back of motor boat ?

• A. $6$ hr, $50$ min
• B. $5$ hr, $40$ min
• C. $7$ hrs
• D. $6$ hr, $30$ min

Answer 1

Answer: (A)

$6$ hr, $50$ min

Let speed of the motor boat is $36$ and speed of the current is $5$.
Speed of boat along with current $=36+5=41$
Distance covered by boat with speed $41$ in $5$ hrs and $10$ min $(5+\frac{10}{60}=\frac{31}{6}h)=\frac{(41\times 31)}{6}=211.83$ km.
Speed of the boat against the current $=36-5=31$
Time taken to covered $=\frac{211.83}{31}=6.83hrs=6$ hrs $50$ min.