Caden, Zoe, Noah, and Sophia shared a pizza. Caden ate 20 percent of the pizza. Zoe ate 50 percent more of the pizza than Caden ate. Noah ate 50 percent more of the pizza than Zoe ate, and Sophia ate the rest of the pizza. Find the percentage of the pizza that Sophia ate.
1. Let the total pizza be represented as 100%.
2. Caden ate 20% of the pizza.
3. Zoe ate 50% more of the pizza than Caden. Therefore, Zoe ate:
   \[
   20\% + 0.5 \times 20\% = 20\% + 10\% = 30\%
   \]
4. Noah ate 50% more of the pizza than Zoe. Therefore, Noah ate:
   \[
   30\% + 0.5 \times 30\% = 30\% + 15\% = 45\%
   \]
5. Adding the percentages eaten by Caden, Zoe, and Noah, we get:
   \[
   20\% + 30\% + 45\% = 95\%
   \]
6. The remaining percentage of the pizza, which Sophia ate, is:
   \[
   100\% - 95\% = 5\%
   \]

The final answer is \(\boxed{5\%}\)