Question

19.为贯彻“激情工作,快乐生活”的理念,

Answer 1

设选手甲答题个数为a

（1）P=P(a=3)+P(a=4)=(2/3)^3+C(3,2)(2/3)^3×(1/3)=16/27.

（2）P(a=3)=(2/3)^3+(1/3)^3=9/27.

P(a=4)=C(3,2)(2/3)^3×(1/3)+C(3,2)(1/3)^3×(2/3)=10/27

a=5时,前面4题对2题错2题 P(a=5)=C(4,2)(2/3)^2(1/3)^2=8/27.

E(a)=107/27.