Question

A boat travels 60km upstream and comes back in 8 hours. What is the speed of the boat, if the speed of stream is 4 km/hr?

• A. 16 km/hr
• B. 20 km /hr
• C. 12 km/hr
• D. 18 km/hr

Answer 1

Answer:

A. 16 km/hr

Speed of Stream$S_s=4km/hr$

$Distance = 60 km$

Let Speed of Boat be X kmph

Speed of boat upstream, $U_s=X-4$

Speed of boat Downstream,$D_s=X+4$

Total Time = 8 hours

$\frac{60}{X+4}+\frac{60}{X-4}=8$

$X^2-15X-16=0$

$X^2-16X+X-16=0$

$(X+1)(X-16)=0$

$X=-1,X=16$

As Speed Can't be negative so, X= 16 kmph.