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.
