Come to the god of probability for help. My head is spinning.

Passing the interview does not mean signing a contract. Three people pass the interview, and the probability of 1 individual failure is c (4 4,3) * (2/3) 3 * (1-2/3) = 32/81.

The probability of four people is: (2/3) 4 = 16/8 1.

The probability of at least 3 people passing the interview: 32/81+16/81= 48/81=16/27.

2)

When Party A and Party B sign the contract, the probability that Party C 1 person passes the interview is (2/3) 3 * c (2,1) * (1-2/3) =16/81.

When Party A and Party B sign the contract, the probability that 0 people from Party C pass the interview is (2/3) 2 * (1-2/3) 2 = 4/81.

The probability of Party B signing the contract: (2/3) 2 * (1-2/3) 2 = 4/81.

Probability of just two people signing a contract:16/81+4/81+4/81= 24/81= 8/27.