SOLUTION: Lily's family took a motor boat 24 km down a river for a picnic. It took them 1 hr to get to the picnic spot. The ride back to the dock took an hour and a half. What was the averag
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Question 736297: Lily's family took a motor boat 24 km down a river for a picnic. It took them 1 hr to get to the picnic spot. The ride back to the dock took an hour and a half. What was the average speed at which the river flowed? What would the boat's average speed be on a lake? Answer by mananth(16946) (Show Source):
Distance against 24 miles distance with 24 miles
t=d/r against current -
24.00 / ( x - y )= 1.50
1.50 ( x - y ) = 24.00
1.50 x - 1.50 y = 24.00 ....................1
24.00 / ( x + y )= 1.00
1.00 ( x + y ) = 24.00
1.00 x + 1.00 y = 24.00 ...............2
Multiply (1) by 1.00
Multiply (2) by 1.50
we get
1.50 x + -1.50 y = 24.00
1.50 x + 1.50 y = 36.00
3.00 x = 60.00
/ 3.00
x = 20.00 mph
plug value of x in (1) y
1.50 x -1.50 y = 24.00
30.00 -1.50 -30.00 = 24.00
-1.50 y = 24.00
-1.50 y = -6.00 kph
y = 4.00
Boat speed 20.00 mph
current speed 4.00 kph
