0次:每种的概率是0.5(反)×0.5(反)×0.5(反)=0.125,共有 C 3 0 =1种情况,因此概率是1×0.125=0.125=1/8;
1次:每种的概率是0.5(正)×0.5(反)×0.5(反)=0.125,共有 C 3 1 =3种情况,因此概率是3×0.125=0.375=3/8;
2次:每种的概率是0.5(正)×0.5(正)×0.5(反)=0.125,共有 C 3 2 =3种情况,因此概率是3×0.125=0.375=3/8;
3次:每种的概率是0.5(正)×0.5(正)×0.5(正)=0.125,共有 C 3 3 =1种情况,因此概率是1×0.125=0.125=1/8.