When formatting Number Objects in Crystal Reports, it's good to know what the currency field can be leveraged to do. The most common use of this is to easily provide a percentage sign, but can be used for explicit strings as well.
Keep in this is effective on a per-field basis.
1. Right-click on the Number field you wish to modify from within the Designer.
2. Select Format Field.
3. Check the "Display Currency Symbol" checkbox.
4. Click Customize.
5. Select the Currency Symbol tab.
6. Modify the Currency Symbol by clicking into it and typing whatever you wish. For starters try a %.
7. Change the Position of the Currency Symbol to be "-123%", meaning that it will appear on the right-hand side of the Number.
8. Ok your way out.
This eliminates the need to use a textbox for the %. Notice also that you can type in pretty much whatever you want into the Currency Symbol, so the sky's pretty much the limit.