RE--計量問題(集合類)

[yenching]

If 55 percent of a group of people have brown hair and 80 percent of the same group do not have red hair, what fraction of those who do not have brown hair have red hair ?

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[scujean]

假設A為所有人數
45%*(1-80%)A/45%A

[pri]

五成五褐髮，八成非紅髮（褐髮亦非紅髮），所以，
五成五褐髮，二成紅髮，四成五其他。答案20%