PEMDAS/BODMAS:
This is a set of rules for order of expressions that is taught to a large number of students at the advance arithmetic and early algebra phases of their schooling. For the expression given in the question it directs:
6/2(1 + 2) = 6/2(3) —Do what is in the parentheses first.
= 6/2(3) — No change because next come handling exponents, of which there are none.
= 3(3) —Do multiplications and divisions in order from left to right.
= 9. —Repeating previous step since there is one division and one multiplication.
There are problems with this set of rules because they were designed for advanced arithmetic and early algebra. They do not handle more advanced expressions. For advanced arithmetic, typically all operations are expressed explicitly, so that 6/2(1 + 2) would not be given, but instead 6/2 × (1 + 2). We will see in the next convention how this distinction can be important, and standard PEMDAS/BODMAS do not distinguish the two expressions