A can finish +A can't finish; B can finish +A and B can't finish; C can finish.

(2)P(x= 1)=q 1，P(x=2)=( 1-q 1)*q2，P(x = 3)=( 1-q 1)*( 1-Q2)，EX=5-2q 1-q2

The first person can finish it,,,

The first one can't finish the second one,,,,

One, two, no, three.

P(X = 1)* 1+P(X = 2)* 2+P(X = 3)* 3

(3)EX=5-2q 1-q2+q 1q2，

=( 1-q 1)(2-q2)+3

Q 1 big, q2 big, E big,

q 1 & gt； Q2, e is very big.