問題一：In how many ways can r-digit quintary sequences (sequences made up of the digits 0, 1, 2, 3, 4) that contain an even number of 1s?
問題二：Suppose a student wants to make up a schedule for a seven-day period which she will study one subject each day. She is taking four subjects: mathematics, physics, chemistry, and economics. We want to know the number of schedules that devote at least one day to each subject?
問題三：In how many ways can 2t + 1 indistinguishable balls place in three distinct boxes so that any two boxes together will contain more balls than the other one?
請問有哪位強者大大可以解出來?????
