+ and -
Press + and - on the right edge with your little finger. Addition and subtraction.
Rest your right hand on 4 5 6 of the numeric keypad and press Enter to start. Press Enter after each number
100+200 350+150 1200-300 980+20 5000-1250 75+25+50 640-40 1+2+3 300-120+45 8800+1200 2500-499 60+75-15 -50 -1200