Question 429237
Let X represent the doctor's original speed. Then his time taken to attend the conference is:200/x. Likewise, his return trip took 200/x-10 hours.  So, our equation looks like:

200/X + 1=200/X-10

Multiplying through by (X)(X-10), we get:
 
200X-2000+X^2-10X=200X
X^2-10X-2000=0
(X-50)(X+40)=0

Solving for X, and tossing out the negative result (-40), we get his speed going there to be 50 mph. His speed coming back was 50-10 mph, or 40 mph.