Question 9

Each fold is made along the line of symmetry perpendicular to the current long edge of the sheet, which halves the longer dimension at each step:

1. Initial dimensions: $20\text{ cm} \times 8\text{ cm}$ (long edge $= 20\text{ cm}$).
2. After 1st fold: Halving the $20\text{ cm}$ edge gives $10\text{ cm} \times 8\text{ cm}$ (long edge is still $10\text{ cm}$).
3. After 2nd fold: Halving the $10\text{ cm}$ edge gives $5\text{ cm} \times 8\text{ cm}$ (now the long edge is $8\text{ cm}$!).
4. After 3rd fold: Halving the current long edge ($8\text{ cm}$) gives $5\text{ cm} \times 4\text{ cm}$.

Therefore, the perimeter of the final $5\text{ cm} \times 4\text{ cm}$ folded sheet is: