create a Total Query. source table of Total query is same as your XTab query:
SELECT Table1.PKField, Sum(Table1.QTY) AS SumOfQTY
FROM Table1
GROUP BY Table1.PKField;
save the query
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now create a nother query that will Join your XTab and the Total Query.
add another column to this query that will calculate the percentage:
SELECT XTAB.*, Query2.SumOfQTY/DSum("QTY","TABLE1") AS Expr1
FROM XTAB LEFT JOIN Query2 ON XTAB.PKField = Query2.PKField;