GMAT Focus Edition — Data Insights: Table Analysis · Graphics Interpretation · Multi-Source Reasoning · Two-Part Analysis
Home Course Data Insights Lesson 9
Data Insights Lesson 9 of 20

Pie Charts &
Part-Whole Analysis

Sectors show percentages. Absolute value = % × total. Two pies with different totals: always compute absolute values before comparing. A largest slice is not a majority unless it exceeds 50%.

45 mins
🎯 DI 70 to 83
📚 Prereq: Lesson 8 (Scatter Plots)
Note: Pie charts show percentages. To find absolute values, you need the total. Comparing two pies with different totals requires computing absolute values, not just comparing percentages.
1

Pie Chart Anatomy

A pie chart shows how a whole is divided into parts. Each sector's arc length (and area) is proportional to its percentage of the total. The key rule: all sectors must sum to 100%.

Market Share Distribution
Market Share
A: 35%
B: 28%
C: 22%
Others: 15%
2

Reading Proportions Precisely

Key Proportion Questions
"Combined share of A and B": Simply add the percentages. A (35%) + B (28%) = 63%.
"Ratio of A to C": 35% : 22% = 35:22 ≈ 1.6:1 or 35/22 ≈ 1.59.
"Does A have majority?": 35% < 50%, so NO. A majority requires >50%.
Remaining = Others: If A+B+C = 85%, then Others = 100%−85% = 15%.
3

Finding Absolute Values

Absolute Value of Sector = Sector % × Total
You MUST have the total (sample size, market size, revenue) to compute absolute values
Example
Total market = $800M. Company A share = 35%.
Company A revenue = 35% × $800M = $280M.
If market grows 10%: new total = $880M. Company A (still 35%) = $308M.
4

Comparing Multiple Pie Charts

Two-Pie Comparison Rules
If totals are EQUAL, a larger sector % means a larger absolute value.
If totals are DIFFERENT, you MUST compute absolute values (% × total) before comparing.
A sector growing from 20% to 25% represents % increase in share — the absolute value could still decrease if the total shrank.
5

10 Pie Chart Traps

⚠ No total = no absolute value

Pie charts show percentages. Without the total, you can't determine how many units any sector represents.

⚠ Two pies, different totals

If Year 1 pie = $100M total and Year 2 pie = $200M total, a 30% sector doubled in absolute size even if the percentage is the same.

⚠ "Majority" means more than 50%

The largest sector is not necessarily a majority. Check if the sector percentage exceeds 50%.

⚠ Adding slices: percentages must sum to 100%

If the given slices sum to less than 100%, there's an "Other" or unlabeled category.

⚠ Visual size illusion

In 3D or tilted pie charts, sectors closer to the viewer appear larger than they are. Always use the labeled percentage.

⚠ Ratio of sectors uses the percentages, not area

A sector twice as large in area has twice the percentage — but confirm with numbers, not visual estimation.

⚠ Comparing across two pies without totals is impossible

You cannot compare absolute values across two pie charts unless you know both totals.

⚠ Percent change of a sector vs. the sector size

Sector share growing from 20% to 22% = +2 percentage points, or +10% relative change of the share.

⚠ "Combined" sectors — watch for double-counting

If asked for "A or B", add their percentages. If asked for "A and B" (overlap), that requires Venn logic — not simple addition.

⚠ Unlabeled sectors

Sometimes sectors are unlabeled. Compute by subtraction: missing % = 100% − sum of labeled sectors.

10 Practice Questions

Q1 of 10
GI~550

A pie chart shows: A=35%, B=28%, C=22%, Others=15%. Total sample = 400. How many respondents are in category B?

Explanation: 112. B = 28% × 400 = 112.
Q2 of 10
GI~600

Using the same pie chart, what is the ratio of A's share to C's share?

Explanation: 35:22. Ratio = A%:C% = 35:22. This cannot be simplified to a clean ratio.
Q3 of 10
GI~600

A pie chart shows that the top 3 companies hold 40%, 25%, and 20% of the market. The total market size is $500M. What is the combined revenue of the three smallest players (the remaining category)?

Explanation: $75M. Top 3 combined: 40+25+20 = 85%. Remaining = 15%. 15% × $500M = $75M.
Q4 of 10
GI~700

Year 1 pie: Company X holds 30% of a $200M market. Year 2 pie: Company X holds 25% of a $320M market. X's absolute revenue:

Explanation: Increased from $60M to $80M. Year 1: 30% × $200M = $60M. Year 2: 25% × $320M = $80M. Even though the market share percentage fell, the absolute revenue grew because the total market expanded significantly.
Q5 of 10
GI~550

A pie chart has 4 labeled sectors: 40%, 30%, 20%, and an unlabeled sector. The unlabeled sector represents:

Explanation: 10%. All sectors must sum to 100%. 40+30+20 = 90%. Unlabeled = 100% − 90% = 10%.
Q6 of 10
GI~650

Two pie charts both show the same market. Year 1: Company A = 45% of a $400M market. Year 2: Company A = 45% of a $600M market. Company A's revenue:

Explanation: Increased from $180M to $270M. Same percentage, but larger total. Year 1: 45% × $400M = $180M. Year 2: 45% × $600M = $270M. When the total grows and share stays constant, absolute revenue grows proportionally.
Q7 of 10
GI~600

A pie chart of expense categories shows: Salaries 45%, Rent 20%, Marketing 15%, Technology 12%, Other 8%. Which TWO categories together equal more than half the expenses?

Explanation: Salaries + Technology = 57%. 45% + 12% = 57% > 50%. This exceeds half. Check others: Rent+Marketing = 35%. Salaries+Technology is the answer.
Q8 of 10
GI~700

A market researcher says: "Since Company B's sector is visually twice as large as Company D's sector in the pie chart, B has twice the revenue of D." This is:

Explanation: Potentially incorrect. In 3D pie charts or tilted perspectives, visual sector sizes can be distorted. Always use the labeled percentage values, not visual estimation. A sector appearing twice as large may only represent 1.6× the percentage.
Q9 of 10
GI~700

A pie chart shows client industry breakdown: Tech 40%, Finance 30%, Healthcare 20%, Other 10%. If the firm has 250 clients, and 60% of Tech clients upgraded their package, how many Tech clients upgraded?

Explanation: 60. Total tech clients = 40% × 250 = 100. Upgraded = 60% × 100 = 60.
Q10 of 10
GI~550

A "donut chart" (pie chart with a hole in the middle) shows the same data as a regular pie chart. Which statement is true?

Explanation: Donut charts convey the same information as pie charts. A donut chart is a pie chart with a hollow center (often used for aesthetic purposes or to display a central label). The sector sizes and percentages are identical to a standard pie chart.
Lesson Summary
Absolute value = % × total

You need the total to compute any absolute count or revenue. Percentages alone cannot answer "how many."

All sectors sum to 100%

Unknown sector = 100% minus all known percentages.

Two pies, different totals: compute absolute values

Never compare percentages across pies unless you confirm the totals are equal.

Majority = more than 50%

The largest sector is not necessarily a majority. It needs to exceed 50% of the whole.