SOLUTION: 1. Two cars leave town at the same time in opposite directions. One travels 35 km/h and the other 40 km/h. In how many hours will they be 200 km apart? 2. Two cars leave town at t

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Question 1014408: 1. Two cars leave town at the same time in opposite directions. One travels 35 km/h and the other 40 km/h. In how many hours will they be 200 km apart?
2. Two cars leave town at the same time in the same direction. One travels 35 mi/h and the other 40 mi/h. In how many hours will they be 15 miles apart?
I can't figure these problems out. It would help out if somebody could help me understand them. My email is alecblake009@hotmail.com

Found 2 solutions by stanbon, josmiceli:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
1. Two cars leave town at the same time in opposite directions. One travels 35 km/h and the other 40 km/h. In how many hours will they be 200 km apart?
The cars are separating at a rate of 35+40 = 75 km/h
Equation:
time = distance/rate
Ans: time = 200km/75km/h = (200/75)hr = 2 2/3 hrs = 2hr 40min
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2. Two cars leave town at the same time in the same direction. One travels 35 mi/h and the other 40 mi/h. In how many hours will they be 15 miles apart?
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slower car DATA: distance = 35t, where t is the number of hours
faster car DATA: distance = 40t,
------
Equation:
faster dist - slower dist = 15
40t - 35t = 15mi
5t = 15 mi
time = 3 hrs
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Cheers,
Stan H.
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Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
All you need is [ distance ] = [ rate ] x [ time ]
Each of the cars needs it's own equation.
Let +d+ = distance traveled by the slower car
until they are +200+ km apart
+200+-+d+ = distance traveled by faster car
until they are +200+ km apart
Let +t+ = time in hrs when they are +200+ km apart
--------------------------
Equation for slower car:
(1) +d+=+35t+
Equation for faster car:
(2) +200+-+d+=+40t+
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Substitute (1) into (2)
(2) +200+-+35t+=+40t+
(2) +75t+=+200+
(2) +t+=+8%2F3+ hrs
(2) +t+=+2+%2B+2%2F3+ hrs
+%282%2F3%29%2A60+=+40+ min
They will be 200 km apart in 2 hrs and 40 min
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check:
(1) +d+=+35t+
(1) +d+=+35%2A%28+8%2F3+%29+
(1) +d+=+93.333+
and
(2) +200+-+d+=+40t+
(2) +200+-+d+=+40%2A%288%2F3%29+
(2) +200+-+d+=+106.667+
(2) +d+=+93.333+
OK
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Be careful in the 2nd problem because the cars get
further apart as time goes on, but not as much as
when they were going in opposite directions
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Let +d+ = distance in miles traveled by slower car
until they are +15+ miles apart
+d+%2B+15+ = distance in miles traveled by faster car
until they are +15+ miles apart
Let +t+ = time in hrs until they are +15+ miles apart
--------------------
Equation for slower car:
(1) +d+=+35t+
Equation for faster car:
(2) +d+%2B+15+=+40t+
--------------------
Substitute (1) into (2)
(2) +35t+%2B+15+=+40t+
(2) +5t+=+15+
(2) +t+=+3+ hrs
In 3 hrs they will be 15 mi apart
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check:
(1) +d+=+35t+
(1) +d+=+35%2A3+
(1) +d+=+105+
and
(2) +d+%2B+15+=+40t+
(2) +d+%2B+15+=+40%2A3+
(2) +d+%2B+15+=+120+
(2) +d+=+105+
OK
Hope this helps