Question 72

A boat can travel in still water at 7 km/h and the speed of the stream is 3 km/h. Find the total time (in hours) taken by the boat to travel 60 km upstream and return to the starting point.

Solution

A boat can travel in still water at 7 km/h and the speed of the stream is 3 km/h.

Speed of boat in still water = B = 7 km/h

speed of the stream = C = 3 km/h

Total time (in hours) taken by the boat to travel 60 km upstream and return to the starting point = $$\frac{60}{B+C}+\frac{60}{B-C}$$

= $$\frac{60}{7+3}+\frac{60}{7-3}$$

= $$\frac{60}{10}+\frac{60}{4}$$

= 6+15

= 21 hours

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