| - The
        aim of using brackets is to join or to group everything that is between
        them.- Multiplication
        signs have priority over addition and subtraction signs, that is,
        when two numbers are joined by the multiplication sign they are inseparable.
        But if they are linked by the addition or subtraction sign, they can be
        separated.
 - We
        must know the properties of the operations so that we don't do anything
        wrong.
 - To
        add up or subtract two numbers they must be separated. 
        We cannot add up two numbers if one of them is linked to another expression
        by means of a multiplication sign.
 - Combined
        operations are solved in several steps. What is not solved in one step
        must be copied as it was, without omitting it or changing its position.
 -
        So, before starting to solve combined operations, we must evaluate the
        expression and plan a strategy to implement what we are going to do
        before and after.
 - As
        a general rule, it is best to solve what is inside the brackets first,
        then do the multiplications and finally do the remaining additions.
 | 
  
    |  | 
        
          | Type
              a
              number  in
              the box below the window. This number must be  
              the result of a part of the expression.You
              must do it step by step. In order to do this,
              you have to delete the previous number.
 When
              you type the right number it will appear in the window. If the typed
              number is not correct it will not appear.
 It
              is not about finding the final result directly.
 |  When you
        click on Init a new expression of combined operations will appear. Solve
        some of them.   |