Posted by **Kim** on Sunday, June 1, 2008 at 12:50am.

A boat travel 4 miles upstream with a current of 5 miles per hour. It takes 40 mminutes longer to go upstream. How fast does the boat go downstream

- algebra -
**drwls**, Sunday, June 1, 2008 at 1:41am
They probably expect you to assume that the boat is using the same power to go through the water in both directions.

Let V be the boat speed relative to the water in both directions. Relative to the shore, its speed is V+5 going downstream and V-5 going upstream.

Let T be the time that it takes to go downstream, in hours. It take T + 2/3 to go upstream. You can write two equations in the two unknowns, V and T.

4 = (V+5) T

4 = (V-5)(T + 2/3)

4 = (V-5)[4/(V+5) + (2/3)]

4(V+5) = 4(V-5) + (2/3)(V^2-25)

40 = (2/3)(V^2-25)

V^2-25 = 60

V^2 = 85

V = 9.22 mph.

Downstream speed = 14.22 mph

Upstream speed = 4.22 mph

Dowstream travel time = 4/14.22

= 0.281 hrs = 16.9 minutes

Upstream travel time = 4/4.22 = 0.948 hr = 56.9 min

## Answer This Question

## Related Questions

- algebra - 36 Upstream, downstream. Junior’s boat will go 15 miles per hour in ...
- algebra - Show a complete solution. Upstream, downstream. Junior’s boat will go ...
- algebra 2 - Kate can row a boat 10 miles per hour in still water. in a river ...
- Algebra - A boat can travel upstream 14 miles in same it can travel downstream 8...
- Intermediate Algebra - in still water, a paddle boat averages 10 miles per hour...
- algebra - A boat can travel 114 miles upstream in the same time that it can ...
- Algebra - The current of a river moves at 3 miles per hour. It takes a boat 3 ...
- Math Algebra - A boat takes 1 hour less to go 200 miles downstream than upstream...
- math - River Current A boat can travel 36 miles upstream in the same time that ...
- MATH - A boat on a river travels 16 miles downstream in only 2 hours. It takes ...

More Related Questions