The circumference of the earth is about 25,000 miles. approximately how far is it from any point on the earth's surface to its center?

Since C = 2rπ
 
if the C of earth = 25000 miles

then the r =  C ÷ (2π)
                = 25,000 miles ÷ 2π
                = 12500 ÷ π
                ≈ 3978.87358 miles

Since radius is a measure of the distance from the center to any point on the circle then that distance would be about 3978.8736 miles