Final answer:
The probability that the number of copper rings is equal to the number of brass rings, with employees and interns pairing up, is 1/10, because the pairs must be formed with all employees together and all interns together, allowing no room for mixed pairs.
Step-by-step explanation:
The student's question deals with a probability scenario where there are an equal number of employees and interns at a company lining up to visit the CEO in pairs. When a pair consists of two employees, they receive a copper ring; a pair of interns receives a brass ring; and a mixed intern-employee pair receives a silver ring. To find the probability that the number of copper rings is equal to the number of brass rings, we must consider the possible ways to pair off the employees and interns so that an equal number of each type of ring is distributed.
Since there are ten each of employees and interns, the only way to satisfy the condition is if there are five copper rings (resulting from five pairs of employees) and five brass rings (resulting from five pairs of interns). This leaves no room for any silver rings and means that every employee must be paired with another employee, and every intern with another intern. Thus, the formation of pairs is fixed, and the probability of this occurring is simply 1, since there are no other pair compositions to consider.
Therefore, the answer is (a) 1/10, as it is the only option consistent with the described scenario.