Question

A boat takes two hours to travel 8 km down and 8 km up the river when the water is still. How much time will the boat take to make the same trip when the river starts flowing at 4 kmph?

• A. 2 hours
• B. 2 hours 40 minutes
• C. 3 hours
• D. 3 hours 40 minutes

Answer 1

The correct option is B 2 hours 40 minutes

When in the direction of current velocity = 8+4= 12
$t_1=\frac{8}{12}=\frac{2}{3}hr$
When against the current velocity 8-4 = 4
$t_2=\frac{8}{4}=2hr$
Total time =$2+\frac{2}{3}=\frac{8}{3}$ hrs = 2 hrs and 40 minutes