This puzzle is designed to make you add too quickly.
The expression is:
15 + 15 × 0 + 5
According to the order of operations, multiplication comes before addition. Start with:
15 × 0 = 0
Now the expression becomes:
15 + 0 + 5
That gives:
20
So the correct answer is 20.
The trap is seeing the first two 15s and immediately thinking 15 + 15 = 30. But the second 15 belongs to the multiplication by zero, so it disappears before the additions are completed.
Answer: 20.
If you got 30, you were probably reading the equation from left to right instead of applying the standard order of operations.
