Posted by **mindy** on Wednesday, April 27, 2011 at 6:49am.

A boat traveled 45 miles downstream (w/ the current) in 3 hours and made the return trop (against the current) in 5 hours. What was the speed of the boat and what was the speed of the current?

- math -
**MathMate**, Wednesday, April 27, 2011 at 8:34am
b=boat (mph)

c=current (mph)

Set up equations using distance=speed*time

3(b+c)=45 ...(1)

5(b-c)=45 ...(2)

Multiply (1) by 5 and (2) by 3:

15b+15c = 225 ...(1a)

15b-15c = 135 ...(2a)

Add (1a) and (2a)

30b+0 = 360

b = 360/30 = 12

Subtract (2a) from (1a)

0+30c = 90

c = 90/30 = 3

Boat speed is 12 mph,

current speed is 3 mph

- math -
**Reiny**, Wednesday, April 27, 2011 at 8:35am
speed of boat ---- x mph

speed of current -- y mph

then :

1. 3(x+y) = 45 or x+y = 15

2. 5(x-y) = 45 or x-y = 9

add them:

2x = 24

x = 12

from one of the others, y = 3

etc.

- math -
**mindy**, Wednesday, April 27, 2011 at 7:00pm
thank you guys so much

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