[Isosceles, inscribed and circumscribed trapezoids]

The perimeter of a trapezoid circumscribed about a circle is 40. Find the midline of the trapezoid.
Since the trapezoid is circumscribed around a circle, the sums of its opposite sides are equal, meaning the sum of the bases is equal to the semiperimeter of the trapezoid, i.e., 20, and the midline of the trapezoid is equal to the half-sum of the bases, i.e., 10.

## Answer

10.00