SOLUTION: A freight train and an express train leave towns 390 km apart, traveling toward one another. The freight train travels 30 km per hour slower than the express train. They pass one a

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Question 132449This question is from textbook Intermediate Algebra
: A freight train and an express train leave towns 390 km apart, traveling toward one another. The freight train travels 30 km per hour slower than the express train. They pass one another 3 hrs. later. What are their speeds? This question is from textbook Intermediate Algebra

Found 2 solutions by checkley71, josmiceli:
Answer by checkley71(8403) About Me  (Show Source):
You can put this solution on YOUR website!
3(X-30)+3X=390
3X-90+3X=390
6X=390+90
6X=480
X=480/6
X=80 KMH FOR THE EXPRESS TRAIN.
80-30=50 KMH FOR THE FREIGHT TRAIN.
PROOF:
3*50+3*80=390
150+240=390
390=390

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
I set up d+=+r%2At for both trains
f = freight train
e = express train
(1) d%5Be%5D+=+r%5Be%5D%2At%5Be%5D
and
(2) d%5Bf%5D+=+r%5Bf%5D%2At%5Bf%5D
----------------------
t%5Be%5D+=+3
t%5Bf%5D+=+3
They both travel for 3 hrs
d%5Be%5D+%2B+d%5Bf%5D+=+390km
d%5Bf%5D+=+390+-+d%5Be%5D
r%5Bf%5D+=+r%5Be%5D+-+30 km/hr
----------------------
(1) d%5Be%5D+=+r%5Be%5D%2A3
(2) 390+-+d%5Be%5D+=+%28r%5Be%5D+-+30%29%2A3
390+-+d%5Be%5D+=+3%2Ar%5Be%5D+-+90
d%5Be%5D+=+480+-+3%2Ar%5Be%5D
substitute this for d%5Be%5D in (1)
3%2Ar%5Be%5D+=+480+-+3%2Ar%5Be%5D
6%2Ar%5Be%5D+=+480
r%5Be%5D+=+80 km/hr
r%5Bf%5D+=+r%5Be%5D+-+30
r%5Bf%5D+=+80+-+30
r%5Bf%5D+=+50 km/hr
The freight train's speed is 50 km/hr
The express train's speed is 80 km/hr
check:
(1) d%5Be%5D+=+r%5Be%5D%2A3
d%5Be%5D+=+80%2A3
d%5Be%5D+=+240+km
(2) 390+-+d%5Be%5D+=+%28r%5Be%5D+-+30%29%2A3
390+-+240+=+%2880+-+30%29%2A3
150+=+150
OK