Question

A boat travels upstream from B to A and downstream from A to B in 3 h. If the speed of the boat in still water is 9 km/h and the speed of the current is 3 km/h, what is the distance between A and B?

• A. 6
• B. 4
• C. 8
• D. 12

Answer 1

The Correct Option is D

Speed of the boat upstream = 9-3 \(=\) \(\frac{6km}{hr}\)

Speed of the boat downstream = 9+3 \(=\) \(\frac{12km}{hr}\)
Let the distance between A and B be x kms.

So,time taken to travel x km upstream by boat \(=\) \(\frac{x}{6hrs}\)

And time taken to travel x kms downstream \(=\frac{x}{12hrs}\) 
According to the question,

\(\frac{x}{6}+\frac{x}{12}=3\)

\(x[\frac{1}{6}+\frac{1}{12}]=3\)

x = 4×3 =12
So, distance between A and B is 12 kms.
So the correct option is (D)