A weighted coin is flipped three times with P(H)=1/3.What is the probability that heads come out exactly twice given hea
问题描述：
A weighted coin is flipped three times with P(H)=1/3.What is the probability that heads come out exactly twice given heads come out at least once?
答
得到0个head的几率是 1*1/3的零次方*2/3的三次方=8/27
得到2个的几率是 3*1/3的二次方*2/3的一次方=2/9=6/27
6/(27-8)=2/7
不懂的话可以追问那最後在答题卡上是怎麽写？？就这么写啊亲我总不能写中文吧～麻烦你拉你就直接写几次方就行了啊我打字更不好打啊