问题
单项选择题
If 75 percent of a class answered the first question on a certain test correctly, 55 percent answered the second question on the test correctly, and 20 percent answered neither of the questions correctly, what percent answered both correctly ？（）
A．10%
B．20%
C．30%
D．50%
E．65%
答案
参考答案：D
解析：
因为20%的学生连一道题也没答对，所以至少答对两道题中的任一道题的比率为80%，所以答对两道题的学生所占的百分比为：55%+75%-80%=50%