pshic! Eight grade question
A motorboat can go 8 miles downstream on a river in 20 minutes. it takes 30minutes for the boat to go upstream the same eight miles. find the speed of the current.
2007-05-21 13:23:43 · 2 answers · asked by مدينا Medina ☪ 6 in Science & Mathematics ➔ Mathematics
Lamicital is rong!
2007-05-21 14:03:49 · update #1
Speed of boat = x miles/min
Speed of current = y miles/min
Distance = 8 miles
Downstream speed = (x + y) miles/min
Upstream speed = (x - y) miles/min
t1 = 8 / (x + y) = 20
t2 = 8 / (x - y) = 30
8 = 20x + 20y
8 = 30x - 30y
-24 = - 60x - 60y
16 = 60x - 60y-----ADD
- 8 = - 120y
y = 1/15
Speed of current = 1/15 miles /min = 4 mph
2007-05-21 23:11:39 · answer #1 · answered by Como 7 · 0⤊ 0⤋
1. Find the speed of the boat downstream.
2. Find speed upstream.
3. Subtract: 1 - 2 = speed of current
1. Let's use mph.
Speed = distance/time
= 8mi/20 min
to go from min to hours, use the conversion 60 min/1 hr
= 8mi/20 min * 60min/1hr
= 24 mph
2. Same thing as above:
8 mi/30 min * 60 min/1 hr = 16 mph
3. Current = 24 mph - 16 mph
= 8 mph
Answer: Current speed is 8 mph
2007-05-21 20:30:33 · answer #2 · answered by Sci Fi Insomniac 6 · 0⤊ 1⤋