Irn Bru maker AG Barr warned that economic conditions continue to be challenging but said it is trading in line with expectations and remains confident of delivering its plans for the full year.Revenue for the quarter ended 31 October increased by 21.4% compared to the same period last year. Like for like sales increased by 10.8%.Total revenue for the nine months to 31 October, 2009 increased by 25% with like for like sales up by 11.2%.Operating margins remain in line with expectations.'The continued strong underlying performance in the core business has been maintained across the third quarter and further growth in the Rubicon brand has ensured we have continued to see good overall year on year performance,' said the group.