C31指3个中取1个形成的组合,其他类比
N=C31*C31+C21*C21+C11*C11
=9+4+1
=14
N总=C61*C61
=36
P=P(都红)+P(都黄)+P(都白)
P=14/36=7/18
E=9/36+4/36*2+1/36*3
=20/36
=5/9
C31指3个中取1个形成的组合,其他类比
N=C31*C31+C21*C21+C11*C11
=9+4+1
=14
N总=C61*C61
=36
P=P(都红)+P(都黄)+P(都白)
P=14/36=7/18
E=9/36+4/36*2+1/36*3
=20/36
=5/9