Answer:
Time spent rowing down stream ![=100\ seconds](https://tex.z-dn.net/?f=%3D100%5C%20seconds)
Speed of boat in still water ![=14\ ms^{-1}](https://tex.z-dn.net/?f=%3D14%5C%20ms%5E%7B-1%7D)
Step-by-step explanation:
Let speed of boat in still water be ![= x\ ms^{-1}](https://tex.z-dn.net/?f=%3D%20x%5C%20ms%5E%7B-1%7D)
Speed of current ![= 10\ ms^{-1}](https://tex.z-dn.net/?f=%3D%2010%5C%20ms%5E%7B-1%7D)
Speed of boat down stream = ![\textrm{Speed of boat in still water +Speed of current}= (x+10)\ ms^{-1}](https://tex.z-dn.net/?f=%5Ctextrm%7BSpeed%20of%20boat%20in%20still%20water%20%2BSpeed%20of%20current%7D%3D%20%28x%2B10%29%5C%20ms%5E%7B-1%7D)
Distance rowed down stream = 2400 m
Time spent rowing down stream =
= ![\frac{Distance}{Speed}=\frac{2400}{x+10}\ s](https://tex.z-dn.net/?f=%5Cfrac%7BDistance%7D%7BSpeed%7D%3D%5Cfrac%7B2400%7D%7Bx%2B10%7D%5C%20s)
Speed of boat up stream = ![\textrm{Speed of boat in still water -Speed of current}= (x-10)\ ms^{-1}](https://tex.z-dn.net/?f=%5Ctextrm%7BSpeed%20of%20boat%20in%20still%20water%20-Speed%20of%20current%7D%3D%20%28x-10%29%5C%20ms%5E%7B-1%7D)
Distance rowed up stream = ![\frac{1}{6} \textrm{ of distance rowed downstream}=\frac{1}{6}\times 2400 = 400\ m](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B6%7D%20%5Ctextrm%7B%20of%20distance%20rowed%20downstream%7D%3D%5Cfrac%7B1%7D%7B6%7D%5Ctimes%202400%20%3D%20400%5C%20m)
Time spent rowing up stream = ![\frac{Distance}{Speed}=\frac{400}{x-10}\ s](https://tex.z-dn.net/?f=%5Cfrac%7BDistance%7D%7BSpeed%7D%3D%5Cfrac%7B400%7D%7Bx-10%7D%5C%20s)
We know that,
So,
![\frac{2400}{x+10}=\frac{400}{x-10}](https://tex.z-dn.net/?f=%5Cfrac%7B2400%7D%7Bx%2B10%7D%3D%5Cfrac%7B400%7D%7Bx-10%7D)
Cross multiplying
![2400(x-10)=400(x+10)](https://tex.z-dn.net/?f=2400%28x-10%29%3D400%28x%2B10%29)
Dividing both sides by ![400](https://tex.z-dn.net/?f=400)
![\frac{2400(x-10)}{400}=\frac{400(x+10)}{400}](https://tex.z-dn.net/?f=%5Cfrac%7B2400%28x-10%29%7D%7B400%7D%3D%5Cfrac%7B400%28x%2B10%29%7D%7B400%7D)
![6(x-10)=x+10](https://tex.z-dn.net/?f=6%28x-10%29%3Dx%2B10)
![6x-60=x+10](https://tex.z-dn.net/?f=6x-60%3Dx%2B10)
Adding 60 to both sides.
![6x-60+60=x+10+60](https://tex.z-dn.net/?f=6x-60%2B60%3Dx%2B10%2B60)
![6x=x+70](https://tex.z-dn.net/?f=6x%3Dx%2B70)
Subtracting both sides by ![x](https://tex.z-dn.net/?f=x)
![6x-x=x+70-x](https://tex.z-dn.net/?f=6x-x%3Dx%2B70-x)
![5x=70](https://tex.z-dn.net/?f=5x%3D70)
Dividing both sides by 5.
![\frac{5x}{5}=\frac{70}{5}](https://tex.z-dn.net/?f=%5Cfrac%7B5x%7D%7B5%7D%3D%5Cfrac%7B70%7D%7B5%7D)
∴ ![x=14](https://tex.z-dn.net/?f=x%3D14)
Speed of boat in still water ![=14\ ms^-1](https://tex.z-dn.net/?f=%3D14%5C%20ms%5E-1)
Time spent rowing down stream =![\frac{2400}{14+10}=\frac{2400}{24}=100\ s](https://tex.z-dn.net/?f=%5Cfrac%7B2400%7D%7B14%2B10%7D%3D%5Cfrac%7B2400%7D%7B24%7D%3D100%5C%20s)