Two people stand on the perimeter of a circular field with radius 10 miles. What is the expected distance between them, in feet?
Note: 1 mile is equivalent to 5280 feet.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Denote the angle of the minor arc between the two people as θ . Note that the distance between the two is given by 1 0 × sin 2 θ × 2 = 2 0 sin 2 θ miles. We now integrate this function from 0 to π in order to calculate the expected value. ∫ 0 π 2 0 sin 2 θ d θ = 2 0 × 2 × ( − cos ( 2 π ) + cos ( 0 ) ) = 4 0 . Now, to calculate the expected distance, we divide this by π , and our distance is π 4 0 miles ≈ 6 7 2 2 7 feet.