Data Interpretation rewards reading before calculating. First read the title, the units, the row and column headings, and the question — only then touch a number. Most errors come from calculating the right thing from the wrong column, or from using the new value as the base in a percentage change.
Worked example: A bar chart shows sales of 100 units in 2020 and 140 units in 2021. The growth is (140 − 100) / 100 × 100 = 40%. The base is always the earlier, original value — dividing by 140 would give about 28.6%, which answers a different question nobody asked.