SOLUTION: a boat travels 1 km upstream and 1 km back. The time for the round trip is 5 hrs. the speed of the stream is 4 km/hr. what is the speed of the boat in still water?
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Question 803333: a boat travels 1 km upstream and 1 km back. The time for the round trip is 5 hrs. the speed of the stream is 4 km/hr. what is the speed of the boat in still water?
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
boat speed x kph
current speed 4 kph
against current x- 4 kph
with current x+ 4 kph
Distance= 1 miles
Time against + time with = 5 hours
t=d/r
1 /( x + 4 ) + 1 /(x - 4 ) = 5
LCD = (x - 4 ) ( x + 4 )
1 *( x - 4 ) + 1 (x + 4 ) = 5 (x^2 - 16 )
1 x - -4 + 1 x + 4 = 5 ( x ^2 - 16 )
2 x = 5 x ^2 -80
5 x ^2 - -2 x - 80
Find the roots of the equation by quadratic formula
a= 5 , b= -2 , c= -80
b^2-4ac= 4 + 1600
b^2-4ac= 1604
x1=( 2 + 40.05 )/ 10
x1= 4.20
x2=( 2 -40.05 ) / 10
x2= -3.80
Ignore negative value
boat speed 4.205 kph
m.ananth@hotmail.ca
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