一道关于概率的英文数学题
7)Aboxcontains3red,4whiteand5bluediscs.Threediscsareselectedatrandom
fromthebox.Findtheprobabilitythat:
a)allthreediscsarethesamecolour,iftheselectioniswithreplacement
b)allthreediscsareofdifferentcolours,iftheselectioniswithoutreplacement
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