Question 1125054
Three possibilities:
1 and 2, not 3, probability is (1/20*7/20*19/20)=133/8000
1 and 3, not 2, probability is (1/20*13/20*1/20) =13/8000
2 and 3, not 1, same as the first one, 133/8000
Overall probability is 279/8000=0.0349