ITPEC FE Subject A April 2026 Question 5

abc×+de×+ — in postfix notation every operator follows its two operands, and the last symbol is the operation performed last.

The two + operators associate left to right, so the expression groups as (a+(b×c))+(d×e):

• •b×c → bc×
• •a+(b×c) → abc×+
• •d×e → de×
• •the outer + joins the two results → abc×+de×+

Answer (c)

Why not others:

• •(a) a+bc×de+× — not valid postfix: the first + has only a before it, so the conversion was left half infix
• •(b) abc×+de+× — evaluates as (a+b×c)×(d+e): adds d and e, then multiplies
• •(d) abc+×de×+ — evaluates as a×(b+c)+d×e: the first + and × swapped places

Key rule: Check a postfix answer by evaluating it with a stack: each operator takes the two values on top, so the expression it rebuilds must equal the original.

Basic Theory · AI-written, may contain errors