Question 81

The respective ratio between speed of the boat upstream and speed of the boat downstream is 3 : 4. What is the speed of the boat in still water if it covers 70 km downstream in 3 hours 30 minutes? (in km/h)

Solution

Let the speed of boat in still water and speed of river be B km/hr and R km/hr respectively

Speed of boat in downstream = (B+R)km/hr

Speed of boat in upstream = (B-R) km/hr

It is given that $$\frac{B-R}{B+R} = \frac{3}{4}$$

we get , B = 7 R

Now it is given that boat covers 70 km in 3.5 hours downstream

so ,

70 = (B+R)3.5

B+R = 20

R = 2.5 km/hr

B = 17.5 km/hr

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