OG11-PS197 黃本

Kath1985

#197
If 75 percent of a class answered the first question on a certain test correctly, 55% 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%
答案為D 但我算出來的是80 因為題目說 兩者都沒做對的是20% 反過來說 兩者都做對就是80%   請問大牛們思路哪裡錯了呢 ?

kingapple25

#197
If 75 percent of a class answered the first question on a certain test correctly, 55% 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%
答案為D 但我算出來的是80 因為題目說 兩者都沒做對的是20% 反過來說 兩者都做對就是80% (那单独做对第1题或者单独做对第2题的去了哪里？)  請問大牛們思路哪裡錯了呢 ?

-- by 会员 Kath1985 (2010/3/3 21:07:27)

kingapple25

应该用55%+75%-(1-20%)

Kath1985

啊  剩下80的是指第一和第二題共同或者各自的做對率 .... 終於搞清楚 謝謝kingapple