How to manage calculation within account dimension where calculation is quantity * rate = value

Hi

There are members in account dimension where calculation is quantity * rate = value.  (Apart from this, other dimensions such as period, entity, version, scenario etc also co-exist)

Account

  Expenses

       Exp 1

       Exp 2

       Exp 3

            Exp 3.1

            Exp 3.2

            Exp 3.3

Calculation of Exp 3.1 to 3.3 is managed by quantity * rate. How do we achieve this calculation.

One way is to create two more children whose calculation is multiplication. But we've 200 such members (3.1 to 3.200). It'll create 400 rate, quantity sub-members. In addition, it'll not be possible to analyse rate or quantity in isolation. So managing this way won't be efficient method of calculation.

For this example, it is as if Exp 3 is product dimension and quantity, rate, value are part of account dimension