Two trains leave a station at the same time, heading in opposite directions. One train is traveling at 80 km/h, the other at 90 km/h. How long will it take for the trains to be 425 km apart?
2006-11-10 10:53:35 · 11 answers · asked by erinmaguireo 1 in Science & Mathematics ➔ Mathematics
Let t be the time, the same time for both then because distance is rate times time the equation is
90t + 80t = 425
170 t = 425
so t = 2.5 hours
2006-11-10 10:57:05 · answer #1 · answered by MollyMAM 6 · 1⤊ 0⤋
mmm.. then after 1 hour they are 170 km apart because 90+80=170, lets make a proportion saying that in 1 hour they are 170 km apart, how long so they are 425 km apart?
170/1=425/x
cross multiply
170x=425
divide by 170
x=2.5
This makes sennse because after 2.5 hours the first train is 200 km apart from the station and the second train is 225. If you add this distances is 425 km.
2006-11-10 19:00:39 · answer #2 · answered by Jose G D 2 · 0⤊ 0⤋
The relative velocity of the two trains is 90+80=170 km/h. So divide 425 km by 170 km/h to find that they will reach the required distance in 2.5 hours.
2006-11-10 18:56:14 · answer #3 · answered by Pascal 7 · 0⤊ 0⤋
relative speed is 80+90=170km/h
time = (1/170)*425 hours
time = 2 hours 30 minutes.
2006-11-10 18:57:30 · answer #4 · answered by DTS 2 · 1⤊ 0⤋
Use the definition for velocity:
v = d/t
so that:
t = d/v
insert the values(with the velocities adding up)
t = 425km/(80km/h + 90km/h)
cancel the kilometers:
t = 425/ 170(1/h)
and there you go:
t = 2.5 h
2006-11-10 19:00:05 · answer #5 · answered by Anonymous · 1⤊ 0⤋
90+80=170..
470/170=2.5
2006-11-10 19:03:39 · answer #6 · answered by arthurfire21 2 · 0⤊ 0⤋
2hrs30mins
each hour the trains have travelled 170km apart
425/170=2.5
2006-11-10 18:59:54 · answer #7 · answered by Anonymous · 1⤊ 0⤋
Easy, let x be the number of hours after they started that the distance = 425
90x + 80x = 425
170x = 425
x = 2.5
After 2.5 hrs.
2006-11-10 18:57:49 · answer #8 · answered by Anonymous · 0⤊ 0⤋
Add the two speeds together, 80km/h + 90km/h = 170km/h. Now divide 170km/h into 425km = 2.5 hours
2006-11-10 19:05:12 · answer #9 · answered by Anonymous · 0⤊ 0⤋
80t + 90t = 425
t is in hours.
2006-11-10 18:56:22 · answer #10 · answered by Anonymous · 0⤊ 0⤋