Question

Aubry's boat goes 20 mph in still water. It travels 75 mi upstream and back in a total time of 8 hr. What is the speed of the current?

Answer 1

The speed of current is 5 mile per hour

Explanation:

Given as :

The speed of boat = x = 20 mph

The distance cover is 75 mile in upstream

Boat goes upstream and back in 8 hours

Let the speed of current = x mph

Now ,

`(75)/(20 - x)+(75)/(20+x)= 8`

Or,
`(1)/(20 - x)+(1)/(20+x)= (8)/(75)`

Or,
`((20+x)+(20-x))/(400-x^(2))=(8)/(75)`

Or,
`(40)/(400-x^(2))=(8)/(75)`

Or, 400 - x² = 375

Or, x² = 400 - 375 = 25

∴ x = √25 = 5 mph

I.e speed of current is 5 mph

Hence The speed of current is 5 mile per hour Answer