(1)
(2)
(1)由茎叶图可知甲班有4人及格,乙班5人及格.
事件“从两班10名学生中各抽取一人,至少有一人及格”记作 A ,则 P ( A )=1-
=1-
=
.
(2) X 取值为0,1,2,3.
P ( X =0)=
=
, P ( X =1)=
+
=
,
P ( X =2)=
+
=
, P ( X =3)=
=
.
所以 X 的分布列为
X
0
1
2
3
P
因此 E ( X )=0×
+1×
+2×
+3×
=
.
(1)
(2)
(1)由茎叶图可知甲班有4人及格,乙班5人及格.
事件“从两班10名学生中各抽取一人,至少有一人及格”记作 A ,则 P ( A )=1-
=1-
=
.
(2) X 取值为0,1,2,3.
P ( X =0)=
=
, P ( X =1)=
+
=
,
P ( X =2)=
+
=
, P ( X =3)=
=
.
所以 X 的分布列为
X
0
1
2
3
P
因此 E ( X )=0×
+1×
+2×
+3×
=
.