Pretty simple - click start, then choose "Easier" or "Harder" mode. Easier mode only adds and subtracts numbers from 1 - 13. Subtraction will not result in negative answers. Harder mode increases the range of numbers for addition and subtraction to 1 - 100 and offers multiplication of numbers 1 -13 and division problems without remainder up to 169 ÷ 13. You can change from one operation to another by clicking on a button any time without affecting your score.
Added algebra
