So the denominator is (P3 takes 1)*(P3 takes 1)/2.

The requirement is that the sum of two balls is 3, so only one ball can be 2 and the other ball can be 1. (Only 1 example! )

So the molecule is 1.

Calculated that the following is 2/9.

The probability of a 2:A miss is 0. 2

B the probability of a mistake is 0. 1

So as long as you want to multiply the above two, the probability of not hitting both is 0. 02

(Never use 1-0.8*0.9) to calculate the probability that two people will miss at least 1.