5. Fashionista Elizabeth has 100 different bracelets, and every day she wears three of them to school. Could it be that after some time, every pair of bracelets has been worn on Liz's wrist exactly once?
Answer: No.

Solution: Consider the first bracelet. It must be paired with each of the other 99 exactly once. Suppose Lisa wears it $n$ days. Then it will be paired with exactly $2 n$ bracelets, which cannot equal 99.