For students who spend most of their time studying from the ETS book and the on-line paper-based tests, you are probably used to seeing four Data Interpretation questions per test.
On the actual test, which has twenty questions per math section, there are only three Data Interpretation questions per section, leading to a total of six Data Interpretation questions on the test (not including the experimental section, if it happens to be Data Interpretation).
I know that was a mouthful, so I’m going to simplify things:
1st math section (20 questions total): 3 Data Interpretation questions
2nd math section (20 questions total): 3 Data Interpretation questions
Total number of Data Interpretation questions: 6
Is there a set number for the type of questions I can see?
Data Interpretation simply means that there is a graph/chart/table and a series of questions relating to graph/chart/table. Each chart/table/graph will have three questions, which is consistent with the above. Meaning, each math section will have one table/chart/graph.
Questions themselves typically draw on percent/fraction/decimal conversion and require some estimation (if you don’t want to fiddle with the calculator). Concepts from statistics, such as mean, median, and mode, also pop up frequently. As to the number of such questions, it is random. The takeaway: know your statistics.
What about the charts/bars/graphs?
On the Data Interpretation section you may see bar charts, you may see a pie graph, you may see a graph with a bunch of funky lines. You might likely see a combination of such graphs for a set of three problems, and will have to combine information from both graphs to answer a question.
There is, however, no clean breakdown in the types of graph. Your best strategy is to prepare as much as possible, so that you will have exposure to almost every kind of graph permutation that the GRE will throw at you.
There will always be exactly three questions per Data Interpretation set. Each math section will feature exactly one Data Interpretation set. Each set of three questions will pertain to the exact same charts/bars/graphs.
There is no solid breakdown in terms of the type of charts/bars/graphs. So make sure to practice as many variants of the charts/bars/graphs to be ready for test day.