SOLUTION: Question #1: A motorboat can move at a speed of 18 km/h in still water. The boat travels 105 km downstream in a river in the same time it takes to go 75 km upstream. What is the s

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Question 109325: Question #1:
A motorboat can move at a speed of 18 km/h in still water. The boat travels 105 km downstream in a river in the same time it takes to go 75 km upstream. What is the speed(or current) of the river?
Question #2:
A small water pipe takes twice as long to fill a tank as does a larger water pipe. With both pipes open, it takes 16 h to fill the tank. Find the time it would take the small pipe working alone to fill the tank.

Answer by checkley71(8403) (Show Source):
You can put this solution on YOUR website!
1) 105/(18+x)=75/(18-x) now cross multiply
75(18+x)=105(18-x)
1350+75x=1890-105x
75x+105x=1890-1350
180x=540
x=540/180
x=3 kh. is the speed of the current.
2) x*2x/(x+2x)=16
2x*2/3x=16 now cross multiply
16*3x=2x^2
2x^2-48x=0
2x(x-24)=0
x=24 hours for the larger pipe to fill the tank.
2*24=48 hours for the smaller pipe.
proof
24*48/(24+48)=16
1152/72=16
72*16=1152
1152=1152