ssas average

I'm trying to replicate the average in the below query using the 'adventureworksDW2012' database.

I'm trying to replicate the average in the below query using the 'adventureworksDW2012' database.

SELECT

avg(SalesAmount/OrderQuantity) as average

sum(salesAmount)assales,

sum(OrderQuantity)asquantity

FROM[dbo].[FactResellerSales]

where

CurrencyKey=(selectCurrencyKeyfromdbo.DimCurrencywhereCurrencyAlternateKey='USD')

andProductKeyin(selectProductKeyfromdbo.DimProductwhereColor='Black')I create a calculation called 'SalesAmountPerUnit' as

[Measures].[Sales Amount]/[Measures].[Order Quantity]

 that calculation gives me the sql equivalent ofSUM(SalesAmount)/SUM(OrderQuantity).                            How do I get the Average of (SalesAmount/OrderQuantity) using MDX or adding a calculated column?             

avg(SalesAmount/OrderQuantity) as average