Originally Posted by RollingBlender

Disclaimer: I am not a math major.
But according to the USGS: :Percent of slope is determined by dividing the amount of elevation change by the amount of horizontal distance covered (sometimes referred to as "the rise divided by the run"), and then multiplying the result by 100. The "run" assumes you're traveling on an idealized flat surface – it does not account for the actual distance traveled once elevation change is factored in."

So, for your 1st example: Divide your round trip distance in half giving you the one-way distance. Convert miles to feet to keep the units the same.
1138 ft / (4.3 miles X 5280ft) = 0.05; 0.05 X 100 = 5% grade. And Bob's yer uncle!