A circular mat with diameter 20 inches is placed on a square tabletop, each of whose sides is 24 inches long. Which of the following is closest to the fraction of the tabletop covered by the mat?
A. 5/12
B. 2/5
C. 1/2
D. 3/4
E. 5/6
Ans. C

我好死了..這樣怎麼去考試啊??
好緊張...求助思路~謝謝!!