word problem pls help

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1)a motor boat can maintain a constant speed of 16km/hr in still water.The boat makes a trip upstream to a certain point in 20min;the return trip takes 15 min. what is the speed of the current?


2) a boat takes 5 hours to make a trip upstream to a camp,on a river that has a current of 3km/hr. It then takes the boat 2.5 hours to make the return trip.How fast did the boat travel relative to the water?


any help would be nice thanks
 
1) Use the standard "uniform rate" equation, "d = rt".

. . . . .upstream:
. . . . .rate: 16 - w
. . . . .time: 20/60 = 1/3
. . . . .distance: (1/3)(16 - w)

. . . . .downstream:
. . . . .rate: 16 + w
. . . . .time: 15/60 = 1/4
. . . . .distance: (1/4)(16 + w)

Since the distances are the same, set their expressions equal and solve for the speed "w" of the water.

2) This one works similarly.

Eliz.
 
stapel said:
1) Use the standard "uniform rate" equation, "d = rt".

. . . . .upstream:
. . . . .rate: 16 - w
. . . . .time: 20/60 = 1/3
. . . . .distance: (1/3)(16 - w)

. . . . .downstream:
. . . . .rate: 16 + w
. . . . .time: 15/60 = 1/4
. . . . .distance: (1/4)(16 + w)

Since the distances are the same, set their expressions equal and solve for the speed "w" of the water.

2) This one works similarly.

Eliz.


hi i am havin some trouble in the equation of this question i got
(1/3)(16-w)=(1/3)(16-w) and dont know what to do next if you could help me it would be great thanks
 
She meant the upstream distance = the downstream distance.
(1/3)(16 - w) = (1/4)(16 + w)
 
Yes, but it is usually cleaner if you multiply both sides by 12.
 
Yes. That gets rid of the fractions. It is easier for most people working with integers.
 
If you put 32 into
(1/3)(16 - w)
It comes out negative so it can't be right.
When you multiply by 12 did you get
16/3-1/3w=4+1/4w
4*16-4w=12*4+3w?
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Gene
 
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