Strong trading at Primark has allowed the owner of the discount clothing chain, Associated British Foods, to raise its full-year results outlook.AB Foods said its adjusted operating profit would be “well ahead of last year”, after Primark enjoyed good trading in the run-up to Easter.Primark’s like-for-like sales – which exclude new store openings – rose 1% over the full year.Despite the upbeat outlook, shares in AB Foods fell 3%.The drop in the company’s shares was put down to disappointment over prospects for future profit margins. AB Foods said margins next year were expected to be similar to this year, whereas some analysts had expected an improvement.AB Foods was the biggest faller on the FTSE 100, although the UK’s benchmark share index was up 35.78 points at 7,413.88 shortly after midday.Shares in AstraZeneca rose 1.9% after the drugs giant reported positive results for two lung cancer treatments.In the FTSE 250 index, shares in troubled infrastructure firm Carillion fell 2% after it announced a number of management changes, including the departure of its chief financial officer, Zafar Khan.The company said Mr Khan would step down with immediate effect. He is being replaced by Emma Mercer, the finance director of its UK construction business.In July this year, shares in Carillion plunged after it issued a profit warning and announced the departure of its chief executive. The company took a £845m provision to cover payment problems on four of its construction contracts.Petra Diamonds dropped nearly 7% after it said a parcel of its diamonds mined in Tanzania had been blocked from export by the country’s government. The company has also suspended operations at one of its mines in Tanzania.On the currency markets, the pound rose 0.2% against the dollar to $1.3219 and was up 0.3% against the euro at 1.1005 euros.