I walked out 10 rods from one of the goal posts and measured the angle from the ground to the top of the post. Then, just to be certain my calculations would be as accurate as possible, I walked another 10 rods in the same direction, and measured the angle again. To be absolutely precise (as I'm a bit of a perfectionist), I walked a final 10 rods in the same direction and measured the angle a third time.
When I went home to calculate the height of the goal post, I was surprised to discover that the sum of my three angles was precisely a right angle.
How tall were the goal posts in rods?