Posted by Rilee on .
A boat travels 1 km upstream and 1 km back. The time for the round trip is 4 hours. The speed of the stream is 5 km/hr. What is the speed of the boat in still water?

Math 
Reiny,
let speed of boat be x mph
time upstream = 1/(x5)
time downstream = 1/(x+5)
1/(x5) + 1/(x+5) = 4
multiply each term by (x+5)(x5)
x+5 + x5 = 4(x^2  25)
2x = 4x^2  100
4x^2  2x  100 = 0
x = (2 ± √1604)/8
x = 5.256 or x = a negative, which would make no sense
the speed of the boat in still water is appr 5.26 mph 
Math 
Jane,
a bout travels 1km upstream and 1 km downstream.it took the boat 1 hour for the round trip. the speed of the current is 2 kph. find the speed of the boat in still water.