Unlike the regular QWERTY keyboard Blackberrys, the 7100 series do not have labelled mathematical symbols. However you can still use your keyboard for performing calculations, below is a list of shortcuts:
Scroll vertically: Hold Alt and roll trackwheel
Display calculation results: Press Enter
Clear screen: Press Y?
Clear last entry: Press T?
Add: Press I?
Subtract: Press U?
Multiply: Press A?
Divide: Press G?