GMAT Data Insights
DI Mindset and Core Math
Select the right information, check units and denominators, and use high-yield arithmetic before calculating.
Mindset
Data Insights is an information-selection task.
Your job is to extract the needed numbers, avoid label and unit traps, and do only the arithmetic required by the question.
Default workflow
Read the question before studying the display.
- 01Identify exactly what is being asked.
- 02Locate only the relevant fields.
- 03Ignore decorative or unrelated data.
- 04Return to the display when a detail is needed.
Universal checklist
Run a five-part check before calculating.
- 01Unit: %, dollars, thousands, per capita.
- 02Timeframe: year, quarter, as of, YoY, Q/Q.
- 03Denominator: per person, per item, per store.
- 04Operation: change, ratio, weighted average, rate.
- 05Precision: exact answer or estimate.
Percent change
Percent change uses the old value in the denominator.
Percent change = (new - old)/old. An increase of 50% means multiply by 1.5; a decrease of 20% means multiply by 0.8.
Weighted average
Weighted averages require the group sizes.
Overall average = (n1*a1 + n2*a2 + ...)/(n1 + n2 + ...). Averaging group averages directly is wrong unless the groups are equally sized.
Rates
Combined rates use total amount divided by total time.
Do not average two rates just because both appear in a table. The weighting comes from how much time or quantity each rate applies to.
Ratio comparison
Ratios can often be compared by cross-multiplication.
To compare A/B and C/D with positive denominators, compare A*D and C*B instead of calculating decimals.
Mini application
Try this: a value rises from 80 to 92. What is the percent increase?
Use the old value as the base.
Solution
The increase is 15%.
Change = 12, and 12/80 = 0.15.
Remember this
Most DI errors happen before the arithmetic.
Confirm unit, timeframe, denominator, and requested operation before touching the calculator.