Ana, The aim of the presentation is to give you the opportunity to demonstrate some original thought and the ability to put across relevant points in a succint and effective manner. There is no question of trying to catch people out, but bear in mind that Detica is a 'brains' type consultancy, and is very selective about recruiting people in its own image.
You will also be interviewed by two senior(ish) staff from the business area(s) your initial interview identified you as being potentially suitable to work in. So expect the interviewers to know their area well and challenge both your understanding and problem solving approaches.
There should be nothing inimidating in this process, and HR should give you a very similar message to the one I have. Just remember that the standard (for any consultancy) is high; prepare well, and if you can demonstrate you have got what it takes you should be fine. Hope this helps, and good luck!