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August 6th, 2015, 02:49 PM   #1
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please help

A motorboat travels 180km in 6 hours going upstream. It travels 288km going downstream in the same amount of time. What is the rate of the boat in still water and what is the rate of the current?

Last edited by skipjack; August 6th, 2015 at 10:33 PM.
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August 6th, 2015, 03:16 PM   #2
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Quote:
Originally Posted by smb43432 View Post
A motorboat travels 180km in 6 hours going upstream. It travels 288km going downstream in the same amount of time. What is the rate of the boat in still water and what is the rate of the current?
upstream ... 180 km in 6 hrs = 30 km/hr

downstream ... 288 km in 6 hrs = 48 km/hr

so, what would you expect the speed to be if there were no current? Use your common sense here.

Last edited by skipjack; August 6th, 2015 at 10:33 PM.
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August 7th, 2015, 12:37 PM   #3
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The harder way: Let v be speed of the boat in still water and r be the speed of the water. The speed of the boat relative to the shore, going upstream, is v- r and going downstream, v+ r. Since speed= distance/time, v- r= 180/6= 30 and v+ r= 288/6= 48.

Add the two equations to eliminate r and solve for v.
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