A unit circle is divided into 12 congruent regions, as shown. What is the perimeter of one of these regions?

7 non-overlapping unit circles are inscribed inside a large circle as shown below. Find the area of the shaded region?

A rectangle of perimeter 44 is partitioned into 5 congruent rectangles as indicated in the diagram. What would be the perimeter of each of the congruent rectangle.

Three circles of unit radius and touching each other. What is max possible area of blue circle as shown in image? And what about red circles?

A circle contains 4 identical squares, as shown below. If each square has a side length equal to 2, what is the radius of the circle?

As shown in the diagram below, circle D is internally tangent to circle A and externally tangent to circles B and C.

If circle B has a radius of 2 and C has a radius of 1, what is the radius of circle D?