30 min = 30/60 hr = 0.5 hr
d = rt
100 = r*0.5
100/0.5 = r
200 = r
r = 200 mph.
We know that Rate = distance/time
(30 minutes is .5 hour)
Rate=100 mile/.5 hour
Divide and we get:
Rate=200 MPH
(Hint: MPH is Miles per Hour---Per means "for each")
Make sense?