8/ 16×7/ 15×6/ 14×5/ 13×4/ 12=6720/524 160= 1/78= 1.28%

(2) The probability of 2 yuan in the lottery:

8/ 16×7/ 15×6/ 14×5/ 13×8/ 12= 1680/43680= 1/39=2.56%

(3) The stall owner can earn 1000 at most, and he doesn't win at least 673 each time;

1000-(20* 1+2*2+0.5*3)/78=673.077