一八九 有个题 说90% of students learn either Geography or A(单词不认识-。-!),and15% lean both, if learn G is the 2 times the percent of the peole learn A, whatis the percent learn G but not A. 选项35%,65%,50%。 (提供者ID:dcrh86。狗主选的是50%) 思路: A+G+B=90% B=15% G+B=2(A+B)èG=2A+B 求G. A+G=90%-15%=75%èA=75%-G G=2A+B=2(75%-G)+15%è3G=165%èG=55%