Because multiplication and division are, in fact, just a shorthand notation of addition/subtraction, only written not with brackets, but with a separate character.

For example, the expression 2+3+3+3+3 you can write it as

2+3*4, or 5+3*3, or 8+3*2 – that is, we take the same action (+3) in parentheses at our discretion and write this parenthesis using a shortened symbol – the multiplication symbol.

Accordingly, when we go in the opposite direction, we perform the action in reverse order – first of all, we “open” this multiplication symbol to a bracket with addition (this, by the way, is literally what computers and calculators do – they only know how to add), and then we start adding all the elements in order.

Because multiplication and division are, in fact, just a shorthand notation of addition/subtraction, only written not with brackets, but with a separate character.

For example, the expression 2+3+3+3+3 you can write it as

2+3*4, or 5+3*3, or 8+3*2 – that is, we take the same action (+3) in parentheses at our discretion and write this parenthesis using a shortened symbol – the multiplication symbol.

Accordingly, when we go in the opposite direction, we perform the action in reverse order – first of all, we “open” this multiplication symbol to a bracket with addition (this, by the way, is literally what computers and calculators do – they only know how to add), and then we start adding all the elements in order.