4. A school coach decided to reward 12 students who ran the distance in the best time. Each of them must be awarded a "gold", "silver", or "bronze" medal. All three types of medals must be used, and the one who finished earlier cannot be awarded a less valuable medal than the one who finished later.

How many ways can the coach distribute the medals (all runners have different times)?
Answer: $C_{11}^{2}=55$.

Solution: see 9th grade.