The basis of this problem is that slope = (vertical distance)/(horizontal distance), also called rise/run
We can set this up as a proportion. I'll use V and H for the distances in the formula
V/H = 8/100 I'm ignoring the negative sign, because it is just telling us that the road is descending.
We know that V = 1000, so we have 1000/H = 8/100
Now we cross multiply, to get 1000x100 = 8H
100,000 = 8H Divide both sides by 8 to get H = 100,000/8 = 25,000 ft.
We aren't finished, though, because we were asked to give the distance in miles.
1 ft = 5,280 mi, so each foot is 1/5280 miles, and 25,000 ft = 25,000x1/5280 = 4.73 miles
