Question

GMAT数学题，求解析过程

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 correc... 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? 求步骤 展开

Answer 1

会画维恩图的话就很简单，建议看看。
下面讲讲直接算的。
只答对first
question的人占总数为A，只答对second
question的人占总数为B，都对的为C，都错的为D。
由题干得
A+C=75
B+C=55
D=20
A+B+C+D=100
前三式相加减第四式就得到了答案。
所以答案是50。