A boat can travel 5 miles downstream in the same lenght of time it travels 3 miles upstream. If the rate of the current is 3 mph, find the speed of the boat in still water. Please if you can do this would you show your work :)
2007-02-25 20:56:59 · 5 answers · asked by Anonymous in Education & Reference ➔ Homework Help
Answer #1, if the boat weren't moving, how could it go anywhere?
Answer #2, if the boat were going 2mph, how could it go up a stream going 3mph?
2007-02-25 21:10:57 · update #1
Awesome! Seemeandsuffer thanks and i get it now so you will get the 10pts after 4 hours is up. Saleem, you were second and you had a little glitch in the addition at the end. No biggie and if you were first i woulda given it to ya. Thanks to both of you though.
RESOLVED
2007-02-25 21:25:22 · update #2
now assume that the speed of the boat in still water is x. now when the boat goes downstream, its effective speed is (x+3) as now the current will also be in the same direction. but when it goes upstream, since the boat has to go against the flow of current, the effective speed is (x-3).
now, time=distance/speed;
time to go upstream=3 / x-3
time to go downstream=5 / x+3
these times are equal.
so ,3 /x-3 = 5 / x+3
cross-multiplying,
5x-15=3x+9
which gives, x=12
2007-02-25 21:17:03 · answer #1 · answered by Anonymous · 0⤊ 0⤋
let the speed of boat in still water be = x mph
speed of stream = 3 mph
hence total speed of the boat while traveling downstream = x+3 mph &
total speed of the boat while traveling downstream = x-3 mph
let the time intervel be = t hours
we have a relation t = d/s
therefore for downstream t = 5/(x+3) & ------------- eq 1
for upstream t = 3/(x-3) ----------------------------------- eq 2
now as eq1 = eq2
therefore 5/(x+3) = 3/(x-3)
on cross multiplication
5*(x-3) = 3*(x+3)
5x - 15 = 3x + 9
5x - 3x = 9 + 15
2x = 26
x = 26/2 = 13 mph
therefore the speed of da boat in still water is 13 mph .
2007-02-25 21:17:18 · answer #2 · answered by saleem 1 · 0⤊ 0⤋
5 miles downstream minus 3 miles upstream = 2 mph in still water.
2007-02-25 21:05:48 · answer #3 · answered by wheeliebin 6 · 0⤊ 1⤋
I'm sorry but I hate this way of putting it in words too.... Find the speed of the boat in still water? if the water is still the boat is still in my opinion... too bad if it's not the right answer:)
2007-02-25 21:02:00 · answer #4 · answered by freebird31wizard 6 · 0⤊ 1⤋
it would help if you have the fomulas given then i can calculate
2007-02-25 21:35:28 · answer #5 · answered by DERECK A 2 · 0⤊ 0⤋