To switch the HP 20b calculator in (Hierarchical) Algebraic mode press [Shift][Mode]. Press [Up Arrow] or [Down Arrow] repeatedly to scroll through the menu till you see " Chain" or " RPN" item is displayed, press [INPUT] key to cycle through till you see “Algebraic”. To exit the Mode menu, press [ON/CE] key once.

In (Hierarchical) Algebraic mode, multiplication and division have a higher priority than addition and subtraction. For example, in (Hierarchical) “Algebraic” mode, pressing 1+2*3 returns a result of 7.00. In Chain mode, the same key presses return a different result.

In (Hierarchical) Algebraic mode, operations have the following priority:

  1. First priority: the power function (y x).
  2. Second priority: combinations and permutations.
  3. Third priority: multiplication and division.
  4. Fourth priority: addition and subtraction.