Question

It takes 3 hours for a boat to travel 27 km upstream and the same boat can travel 30 km downstream in 2 hours. The speed of the boat is 12 km/hr

• A. True
• B. False

Answer 1

Answer: (A)

Let speed of boat be x km/hr

Let speed of current be y km/hr

$\therefore$ upstream speed = x - y km/hr

downstream speed = x + y km/hr

Speed = $\frac{distance}{time}$

Then according to the first condition

$\frac{27}{x-y}=3$ $\Rightarrow$ x - y = 9..........(i)

Then according to the second condition

$\frac{30}{x+y}=2$ $\Rightarrow$ x + y = 15..........(i)

adding (i) and (ii)

2x = 24

$\Rightarrow$ x = 12 km/hr

substitute x = 12 in (i) we get

y = 3 km/hr