slope and fractions

Question

When driving down a mountain road you notice signs that say a 8% grade. This means that the slope of the road is -8/100. Approximate the amount of horizontal change in your position if your elevation has descended 1800 feet.

Answer 1

slope (m) is equal to rise(vertical change)/run(horizontal change).

if your slope is -8/100 then you get the following.

for every 8 feet downward you move 100 feet horizontally.

you can set this up as a proportion as follows:

-8/100 = -1800/x

solver for x:

x(-8/100)=-1800 => x = -1800*(100/-8)

x=22500 ft horizontally