5. The 11 letters of 'IMOHKPRELIM' are written on 11 cards (one letter on each card). If three cards are randomly drawn, how many different combinations of the three letters are there? (Order is not considered. For instance 'IMO' and 'IOM' are regarded to be the same combination.)
現把「IMOHKPRELIM」這 11 個英文字母分別寫在 11 張卡紙上（每張卡紙寫上一個字母）。若隨意抽出三張卡紙, 所抽出的三個英文字母有多少個不同組合?（不考慮次序, 例如 $\ulcorner\mathrm{IMO} 」$ 和 $\ulcorner\mathrm{IOM} 」$ 視為相同組合。）
5. 100
5. Note that there are 9 different letters, with 'I' and 'M' occurring twice. If the three letters are distinct, there are $C_{3}^{9}=84$ combinations. Otherwise, there are either two 'I's or two 'M's, plus one of the remaining 8 letters. There are $2 \times 8=16$ such combinations. Hence the answer is $84+16=100$.