As others have said, it is just convention. The convention relies on an implied order for summation and multiplication, and that can get you into trouble if you're not careful to provide the explicit order. For example, when for part of your problem, you come up with the equation X = 2Y + 4. In another part, you discover that Y = X + 4. You substitute X+4 for Y in the first equation and you come up with X = 2X + 4 + 4. This is wrong, but a student early in their learning might not immediately understand why. I should have used brackets/parenthesis around the substitute term when I replaced the variable. X = 2[X+4] + 4

If the implicit order of operations (the "DMAS" part of "BEDMAS") is causing you problems, I suggest eliminating it before you start working on the problem. Translate the problem from an implicit order of operation to an explicit order of operations: BRACKET ALL THE THINGS!

X = 2Y + 4 <-- Nah.

[X] = [ [2 * Y] + [4] ] <-- Yes!

It might be a crutch, like counting on fingers to add or subtract, but it was the only thing that worked for me. I still use it when I'm not completely sure that Excel and I agree on the implicit order in a formula.