This math puzzle is another example of why the order of operations matters. The equation looks simple, but multiplication must be completed before any addition. That one rule completely changes the result compared with solving strictly from left to right.
First calculate 30 × 0. Any number multiplied by zero equals zero, so the equation becomes 20 + 0 + 1. Now add the remaining numbers and you get 21. Therefore, the correct answer is 21.
Many people are tempted to add 20 and 30 first, but that is not how the standard order of operations works. Multiplication always comes before addition unless parentheses tell you otherwise.
If you answered 21 right away, you spotted the zero trap and followed the rule correctly. It is a short puzzle, but it catches plenty of people who answer too quickly.
