August 6th, 2015, 03:49 PM | #1 |
Newbie Joined: Oct 2012 Posts: 6 Thanks: 0 | 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 11:33 PM. |
August 6th, 2015, 04:16 PM | #2 | |
Math Team Joined: Jul 2011 From: Texas Posts: 3,093 Thanks: 1675 | Quote:
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 11:33 PM. | |
August 7th, 2015, 01:37 PM | #3 |
Math Team Joined: Jan 2015 From: Alabama Posts: 3,264 Thanks: 902 |
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. |