This equation is a classic source of arguments because the notation can look more confusing than it really is.
The expression is:
12 ÷ 3(1 + 3)
Start with the parentheses:
1 + 3 = 4
That leaves:
12 ÷ 3 × 4
Under the standard modern order of operations, multiplication and division have equal priority, so they are handled from left to right:
12 ÷ 3 = 4
4 × 4 = 16
So the conventional answer is 16.
Some people interpret the original notation as 12 ÷ [3(1 + 3)], which would produce 1. That is why adding clearer parentheses removes the ambiguity.
Answer under the standard left-to-right convention: 16.
