ITPEC FE Subject A April 2026 Question 5

Postfix notation — the operator is written after its two operands.

Because + is left-associative, a+(b×c)+(d×e) groups as ((a+(b×c))+(d×e)). Convert bottom-up:

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

Answer (c): abc×+de×+

Why not others:
- (a) a+bc×de+× — leaves the first + in infix position and ends with ×, which would multiply two sums
- (b) abc×+de+× — applies + to d and e where the expression has ×, then multiplies at the end
- (d) abc+×de×+ — evaluates a+b before the multiplication, i.e. (a+b)×c

Key rule: Each operator in postfix acts on the two most recent results, so the last symbol is always the final operation — here the outer +, never a ×.

AI-generated — may contain errors