Cowboy Bob owns a used car lot. There are currently 40 cars on his lot and the mean weight of those cars
is 3,200 pounds. Cowboy Bob sells 5 of the cars, and
the mean weight of the remaining cars is then 3,100
pounds. What is the mean weight, in pounds, of the 5
cars that were sold?

Given:

the climber is at 2.5 miles above sea level
the earth's radius is 3959 miles
we need to determine the climber's distance to the horizon. 

let r = radius of the earth
      d = distance to the horizon

use the pythagorean theorem to solve for the distance of the climber to the horizon. the two legs of the right triangle are the radius of the earth and the distance of the climber to the horizon. 

r^2 + d^2 = (r + 2.5)^2

3959^2 + d^2 = (3959 + 2.5)^2

solve for d:

d = 208.68 miles

therefore, the climber is 208.68 miles from the horizon.