NO.PZ2016012101000128
问题如下：
Assuming no changes in other variables, which of the following would decrease ROA?
选项：
A.A decrease in the effective tax rate.
B.A decrease in interest expense.
C.An increase in average assets.
解释：
C is correct.
Assuming no changes in other variables, an increase in average assets (an increase in the denominator) would decrease ROA. A decrease in either the effective tax rate or interest expense, assuming no changes in other variables, would increase ROA.
解析：根据题目解释，这道题是根据ROA=NI/asset来计算的，更严谨的公式是ROA= [NI+int(1-t)]/asset，不管是哪个公式，C选项都能选出来，分母增加肯定会导致ROA变小。
如果用简化的公式，interest expense降低会增加分子NI，ROA变大，如果用分子是NI+int(1-t)的公式，NI中扣掉了利息费用，然后又加回来，一减一增抵消了利息费用，ROA不变，所以不管用哪个公式，B都不对。
effective tax rate变小，简化的公式，NI变大，ROA变高，严谨的公式分子也是变大的，所以A不对。
如题
