20-12:3

To solve the expression \( 20 - 12 : 3 \), we need to follow the order of operations, which is often remembered by the acronym PEMDAS (Parentheses, Exponents, Multiplication and Division (from left to right), Addition and Subtraction (from left to right)).

Here, we first perform the division:

1. Calculate \( 12 : 3 \) (which is the same as \( 12 \div 3 \)): \[ 12 \div 3 = 4 \]

2. Then substitute this back into the expression: \[ 20 - 4 \]

3. Finally, perform the subtraction: \[ 20 - 4 = 16 \]

So, \( 20 - 12 : 3 = 16 \).