作业帮SAT概率题求解答Five red balls and two blue balls are placed in an empty box.One ball a time is to be selected randomly and removed 4 balls from the box.What is the probability that the first two balls removed will be red and third ball removed
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SAT概率题求解答Five red balls and two blue balls are placed in an empty box.One ball a time is to be selected randomly and removed 4 balls from the box.What is the probability that the first two balls removed will be red and third ball removed
SAT概率题求解答
Five red balls and two blue balls are placed in an empty box.One ball a time is to be selected randomly and removed 4 balls from the box.What is the probability that the first two balls removed will be red and third ball removed will be blue?
A 4/21 B 2/21 C 5/8 D 5/7 E 3/42
最好能用组合或者排列的那个Pmn Cmn的公式做，
SAT概率题求解答Five red balls and two blue balls are placed in an empty box.One ball a time is to be selected randomly and removed 4 balls from the box.What is the probability that the first two balls removed will be red and third ball removed
5/7*2/3*2/5=4/21
选A