NO.PZ202106160300001102
问题如下：
A fixed-income portfolio manager creates a contingency table of the number of bonds held in her portfolio by sector and bond rating. The contingency table is presented here:
The relative frequency of AA rated energy bonds, based on the total count, is closest to:
选项：
A.10.5% B.31.5% C.39.5%解释：
A is correct. The relative frequency for any value in the table based on the total count is calculated by dividing that value by the total count. Therefore, the relative frequency for AA rated energy bonds is calculated as 85/806 = 10.5%.
B is incorrect because 31.5% is the relative frequency for AA rated energy bonds, calculated based on the marginal frequency for all AA rated bonds, so 85/(32 +25+85 +100 +28), not based on total bond counts.
C is incorrect because 39.5% is the relative frequency for AA rated energy bonds, calculated based on the marginal frequency for all energy bonds, so 85/(100+ 85 + 30), not based on total bond counts.
以及这个只能死算是吧？一个一个加总。
