It takes a couple four hours to row 28 miles with the river current. If it takes them 7 hours to cover the same distance when rowing against the current, find the speed of the river current.
2007-09-19 13:52:35 · 5 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
1.5mph is current speed
7 mph w/ current
4 mph against
x=current speed
y=their speed
7-x=y
4+x=y
7-x=4+x
2x=11
y=5.5
7-x=5.5
x=7-5.5=1.5
4+x=5.5
x=5.5-4=1.5
2007-09-19 14:01:49 · answer #1 · answered by Anonymous · 0⤊ 0⤋
Let
b = speed of boat in still water
r = speed of river current
distance = rate * time
4(b + r) = 28
b + r = 7
7(b - r) = 28
b - r = 4
So we have:
b + r = 7
b - r = 4
Subtract the second equation from the first.
2r = 3
r = 3/2 = 1.5 mph
The speed of the river current is 1.5 mph.
2007-09-19 21:01:53 · answer #2 · answered by Northstar 7 · 0⤊ 0⤋
speed when rowing with river
28/4=7mph
speed when rowing against river
28/7=4mph
difference in speed should be the speed of the current
7-4=3mph
???
2007-09-19 21:00:15 · answer #3 · answered by jf_yao87 2 · 0⤊ 1⤋
Previous answer is OK except for the final bit.
Speed of current is 1.5 mph. They go faster by 1.5 in one direction, slower by 1.5 in the other.
.
2007-09-19 21:03:15 · answer #4 · answered by tsr21 6 · 0⤊ 0⤋
Please do your own homework! We are not here to answer homework questions. That is cheating!
2007-09-19 20:59:59 · answer #5 · answered by UPESKYMO 5 · 0⤊ 1⤋