Math Problem (Level 3) : Area ratio divided in sector (JJJ11)

There is the sector OAB which is 1/4 part a circle.

Answer the following questions.

Pi is assumed to be 3.14.

(1) Find the ratio of the area of a shadow area and the sector OAB in Fig. 1.

Noted that the straight lines OA, CD, and EF are parallel.



(2) As shown in Fig. 2, the straight line parallel to OA was drawn from each point which divided the arc AB of the sector OAB into five equally. OA is 5 cm.

Find the sum of the area of two shadow areas.




Answer
(1) 4 : 9
(2) 7.85 cm2

Reference