1、P=5/(5+10)=1/3
2. x=0 ,P=C3/10/C3/15=24/99
x=1 ,P=(C2/10 * C1/5 )/ C3/15=45/91
x=2 ,P=(C1/10 × C2/5 )/ C3/15=20/91
x=3 ,P=C3/5 / C3/15=2/91 期望=0×24/99+1×45/91+2×20/91+3×2/91=1
请在15分钟内作出此概率体答对有奖
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1、P=5/(5+10)=1/3
2. x=0 ,P=C3/10/C3/15=24/99
x=1 ,P=(C2/10 * C1/5 )/ C3/15=45/91
x=2 ,P=(C1/10 × C2/5 )/ C3/15=20/91
x=3 ,P=C3/5 / C3/15=2/91 期望=0×24/99+1×45/91+2×20/91+3×2/91=1