Question 11
Betty the beaver plays with cards bearing the strings ABBA, GAGA, GIBB and IGGY. She places cards consecutively or overlaps them to obtain other special strings.
For example, Betty can form GIABIGGYGA as follows:
- Put the GIBB card on the table.
- Partly overlap the first card with ABBA: GIABBA.
- Place GAGA to obtain GIABBAGAGA.
- Place IGGY on this sequence to obtain GIABIGGYGA.
Betty has very many such cards. Which of the following strings can she certainly not form?
For example, Betty can form GIABIGGYGA as follows:
- Put the GIBB card on the table.
- Partly overlap the first card with ABBA: GIABBA.
- Place GAGA to obtain GIABBAGAGA.
- Place IGGY on this sequence to obtain GIABIGGYGA.
Betty has very many such cards. Which of the following strings can she certainly not form?