To find the number of shelves, you can divide the total number of cupcakes by the number of cupcakes on each shelf.
Given:
- Total cupcakes = 20
- Cupcakes per shelf = 5
The calculation is:
\[ \text{Number of shelves} = \frac{\text{Total cupcakes}}{\text{Cupcakes per shelf}} = \frac{20}{5} = 4 \]
Therefore, there are 4 shelves.