SOLUTION: A 150 minute river cruise goes 14km upstream and then back again. The river has a current of 3km an hour going downstream. What is the boat's speed in still water and how long was

Question 937920: A 150 minute river cruise goes 14km upstream and then back again. The river has a current of 3km an hour going downstream. What is the boat's speed in still water and how long was the upstream journey in minutes?
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
boat speed x km Time forward + time return = hours
current speed 3 km

against current x- 3 km/h
with current x+ 3 km/h

Distance= 14 km

Time against + time with = 2.5 hours
t=d/r

14 /( x + 3 ) + 14

LCD = (x - 3 ) ( x +
14 *( x - 3 ) + 14
14 x - -42 + 14 x +
28 x = 2.5 x ^2 -22.5
2.5 x ^2 - -28 x - -22.5 =

Find the roots of the equation by quadratic formula

a= 2.5 , b= -28 , c= -22.5

b^2-4ac= 784 + 225
b^2-4ac= 1009

x1=( 28 + 31.76 )/ 5
x1= 11.95

x2=( 28 -31.76 ) / 5
x2= -0.75
Ignore negative value
boat speed 11.953 km/h
Time upstream = (14/8.953)*60 =94 minutes

m.ananth@hotmail.ca

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