SOLUTION: An express train and a a local train start out from the same point and travel in opposite directions. The express train travels twice as fast as the local train. If they are 480 mi

Question 152556: An express train and a a local train start out from the same point and travel in opposite directions. The express train travels twice as fast as the local train. If they are 480 miles apart, after 4 hours, what is the average speed of each train?
Answer by mducky2(62) (Show Source): You can put this solution on YOUR website!
One equation might be particularly useful:
Speed * Time = Distance

We can shorten these into variables we need:
speed of the express train = s_e
speed of local train = s_l

Using the information from the problem. Both trains traveled the same time. We also know the total distance:
time = 4 hours
total distance = 480 miles

Now let's use the information we know. Since the express train travels twice as fast as the local train, we can set the speed of the express train in terms of the local train:
s_e = 2_l

Let's plug it all back into the original equation:
Speed * Time = Distance
(s_e + s_l) * 4 = 480
(s_e + s_l) = 120

Since s_e = 2_l
2s_l + s_l = 120
3s_l = 120
s_l = 40 mph

The average speed of the local train is 40 mph.

Now we can solve for the speed of the express train.
s_e = 2_l
s_e = 2(40)
s_e = 80 mph

The average speed of the express train is 80 mph.

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