SOLUTION: Two trains travel at right angles to each other after leaving the same train station at the same time. One hour later they are 100 miles apart. If one travels 20 miles per hour fa

Let  = the distance the slower train had gone after 1 hour.
Let  = the distance the faster train had gone after 1 hour.



Then by the Pythagorean theorem



Let the rate of the slower train be r.
Then the rate of the faster train is r+20. 

Using 





So



becomes:







Divide thru by 2



Factoring:









We ignore the negative rate.

So the rate of the slower train is r = 60 mi/h

Therefore the rate of the faster train is r+20 = 60+20 = 80 mi/h

So you were right!  The answer is 80 mi/hr

Edwin