※ 引述《z031096782 (黯淡)》之銘言：
: thirty cars were assembled in a factory. The options available were a radio,
: an air conditioner, and white-wall tires. It's known that 15 of the cars have
: radios, 8 of them have air conditions, and 6 of them have white-wall tires.
: Moreover, 3 of them have all three options, We want to know at least how many
: cars do not have any options at all.
令所求(三項裝備都還沒裝的)為X
A集合=有radio的
B集合=有空調的
C集合=有輪胎的
由排容原理求出
A∪B∪C=A+B+C-(A∩B+B∩C+A∩C)+A∩B∩C
=15+8+6-(A∩B+B∩C+A∩C)+3
=32-(A∩B+B∩C+A∩C)
∵(A∩B+B∩C+A∩C)≧9
∴A∪B∪C≦23
共30台車
∴A∪B∪C+X=30
∴X≧7
有錯請見諒
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