This is the third portion of the section, and quite a few DS questions were asked in the last CAT paper.
Data Sufficiency problems usually take the form of a logical puzzle, and are in the form of a question followed by two statements. You need to answer whether you can solve the problem using the statements individually, or using both, or whether you cannot solve the problem using the information provided.
The key to answering such problems is to pretend like one statement does not exist, try solving the problem, and then pretend like the other statement does not exist and try solving the problem again. These problems are generally tricky, and I would recommend lots of practice and perhaps solving them near the end of your section, after you have solved the other problems.
The DI/LR section is one of the higher scoring sections on the CAT, so you can look to it for help in improving your overall score as well, as long as you devote a good proportion of your time to it.
Although recent CATs have had 4-5 question sets, be prepared for 1-2 question sets as well. DS questions have never appeared in sets. Important things to remember while attempting this section are that you need be quick in switching sets if you find a particular set tough, and you need to have presence of mind while solving DI/LR questions.
Both of these things can be achieved with the help of practice with MOCK TESTS
CAT 2012 exam is being conducted from October 11, 2012 to November 6, 2012 with a test window of 21 days.