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Scheduling five students into fifteen slots

Question

Over the coming month there are 1515 meeting slots, and you need to meet each of 55 students exactly 33 times, one student per slot, so every slot gets used. One particular student cannot make the first slot. How many valid schedules are there?

Short answer

134,534,400134{,}534{,}400. A schedule is a word using each of the five student labels three times, so there are 15!(3!)5\tfrac{15!}{(3!)^5} in total. By symmetry each student is equally likely to occupy slot one, so 45\tfrac45 of these avoid the restricted student there: 45⋅168,168,000\tfrac45\cdot168{,}168{,}000.

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