Question

Choose the most appropriate option.
A boat travels upstream from A to B and back from B to A in $5$ hours. The speed of the boat in still water is $8$ km/hour and the speed of the current is $4$ km/hour. Then, the distance from A to B is:

• A. $9$ kms.
• B. $10$ kms.
• C. $12$ kms.
• D. $15$ kms.

Answer 1

The correct option is D $15$ kms.

Speed of the boat at down stream $=(8+4)km/hr=12km/hr$

Speed of the boat at upstream $=(8-4)km/hr=4km/hr$

Let distance between $A$ to $B$ be $x$

$\therefore$ $\frac{x}{4}+\frac{x}{12}=5$

$\Rightarrow$ $3x+x=60$

$\Rightarrow$ $4x=60$

$\therefore$ $x=15km$