Data interpretation gives you a chart or table and asks several questions about it. It is the most reliably winnable part of GRE Quant, and it is where careless students lose marks they were never going to lose on the mathematics.
Read the furniture before the data. Before the first question: the title, both axis labels, the units, the scale, and any footnote. Thirty seconds here prevents the three commonest errors — reading thousands as millions, reading a percentage of one total as a percentage of another, and missing that a scale does not start at zero.
Know which question you are being asked. These are the four shapes, and they are easy to confuse under time:
- a value — read it off
- a difference — subtract, and check which way round
- a percentage change — the denominator is the ORIGINAL value, always
- a share of the total — and the total may itself need computing
Percent change versus percentage points. Going from 20% to 30% is a rise of ten percentage points and a rise of fifty per cent. The option that says both numbers will be there.
Estimate first. The options in a data-interpretation set are usually far enough apart that a rounded calculation settles it. Compute precisely only when two options survive.
Do not carry assumptions between questions. Each question in a set is independent. A total you computed for question one is reusable; an assumption you made to answer it is not.