Problem: A boat in the water has a speed of 20 km/h....

[Alfredo]

A boat in the water has a speed of 20 km/h.The boat needs 5 h to travel 48 km in a river and then come back to the starting point. What is the speed of the stream. The answer is 4 km/h.
I tried to set the equation (48×2)/(20-x)=5 where x is the speed of the stream but it doesn't work.Can you help me please?

 

[Harry_the_cat]

I find a table helps with these speed/distance/time type of problems. Given that the total time is 5 hours, the appropriate equation can be formed and then solved.

	Speed	Distance	Time
With current	20+x	48	\(\displaystyle \frac{48}{20+x}\)
Against current	20-x	48	\(\displaystyle \frac{48}{20-x}\)
		Total time	5

 

[Alfredo]

You are right i just calculated agains current

 

[Alfredo]

I find a table helps with these speed/distance/time type of problems. Given that the total time is 5 hours, the appropriate equation can be formed and then solved.

	Speed	Distance	Time
With current	20+x	48	\(\displaystyle \frac{48}{20+x}\)
Against current	20-x	48	\(\displaystyle \frac{48}{20-x}\)
		Total time	5

Thank you