SOLUTION: Having trouble finding the right formula! How do I solve? An express and local train leave Gray's Lake at 3 P.M. and head for Chicago 50 miles away. The express travels twice as

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Question 171435: Having trouble finding the right formula! How do I solve?
An express and local train leave Gray's Lake at 3 P.M. and head for Chicago 50 miles away. The express travels twice as fast as the local, and arrives 1 hour ahead of it. Find the speed of each train.
Answer by Mathtut(3670) About Me  (Show Source):
You can put this solution on YOUR website!
d=rt. we know the distance in both cases is 50. Lets call the local trains rate r and its time t. So the express's rate would be 2r and its time t-1
:
50=rt..........eq 1
50=2r(t-1).....eq 2
:
lets rewrite eq 1 as t=50/r and plug that value into eq 2
:
50=2r%28%2850%2Fr%29-1%29----->50=2r%28%2850-r%29%2Fr%29----
50=2cross%28r%29%2850-r%29%2Fcross%28r%29
50=100-2r---->-2r=-50
highlight%28r=25%29MPH-speed of the local train
highlight%282%2825%29=50%29MPH-speed of the express
: