21. 甲、乙、丙三箱中都裝有藍色的球與紅色的球，甲箱中有 3 顆藍球、2 顆紅球，乙箱中有 2 顆藍球、2 顆紅球，丙箱中有 1 顆藍球、5 顆紅球。今從三箱中各取一球，若至少取得 2 顆紅球的機率為 p，則下列何者正確？
(A)
【用戶】康靖坤
【年級】國二下
【評論內容】三紅機率 = (2/5)(2/4)(5/6) = 20/120兩紅一藍機率 = (3/5)(2/4)(5/6) + (2/5)(2/4)(5/6) + (2/5)(2/4)(1/6) = 54/120p = 20/120 + 54/120 = 74/120答案應是 (D) 才對
【用戶】康靖坤
【年級】國三上
【評論內容】三紅機率 = (2/5)(2/4)(5/6) = 20/120兩紅一藍機率 = (3/5)(2/4)(5/6) + (2/5)(2/4)(5/6) + (2/5)(2/4)(1/6) = 54/120p = 20/120 + 54/120 = 74/120答案應是 (D) 才對