Final answer:
The expression "3 groups of 12" is represented by the multiplication equation 3 × 12, which equals 36.
Step-by-step explanation:
The expression that represents 3 groups of 12 is 3 × 12. This is a basic multiplication problem where the number 3 indicates the quantity of groups and the number 12 indicates the number of items in each group. To solve it, you multiply 3 by 12, which gives you the total number of items in all 3 groups combined. Therefore, 3 × 12 equals 36. This type of expression is fundamental in understanding how multiplication represents repeated addition and is a common concept taught in mathematics at the middle school level.