Reverse polish notation (rpn), sometimes referred to as postfix notation, is a way of writing mathematical expressions where each operand is preceded by the two operators it applies to and looks something like 2 5 3 + * instead of (5 + 3 ) * 2
What does this have to do with scientific calculators ?Well, it turns out that it is easier/more efficient for computers to parse an RPN expression than an infix one. In fact, if you look at the code underlying most calculators you'd find that most of them take the infix expressions that we write and first convert them to postfix before evaluating them. Meta calculator's graphing and scientific calculators both do exactly this. If you'd like some insight into how a calculator typically would evaluate a reverse polish notation expression, try our interactive rpn calculator .
What are some examples of RPN? 
Infix Version  RPN Version 
3  2  3 2  
3 * 2+5  5 3 2 * + 
(12  3 ) /3  12 3  3 / 

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Postfix  Value 
3 11 +  
3 11 5 +   
3 11 + 5   
2 3 11 + 5 *  
9 5 3 + 2 4 ^  + 
Ok, now that you've seen some examples, try these practice problems out!
Infix Version  RPN Version  Value 
5 + 2 ^3  13  
3 * 2 11  5  
2 + 1  12 /3  1  
( 6  3) ^2  11  2  
6  3 ^2  11  14  
162 / (2 + 1 ) ^4  2 