GMAT · Graphics Interpretation · TOPIC LESSON
Compute comparisons while respecting weights, overlaps, uncertainty and response constraints.
BY THE END, YOU CAN
BEFORE YOU START
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01 / UNDERSTAND & APPLY
A Graphics Interpretation response often contains more than one blank. Determine the target and available choices for each before doing arithmetic. Choices can help decide how much precision is needed, but must not replace correct interpretation.
The original growth figure records monthly revenue in thousands of dollars at months 0,1,2,3: Firm P has 20,30,40,50; Firm Q has 60,65,70,75. Each adjacent pair is one month apart. The points are observed totals; connectors guide the eye.
Full-size scientific diagram. Swipe or scroll horizontally; keyboard users can focus the diagram and use arrow keys.
ORIGINAL WORKED EXAMPLE
Growth figure, month 2: What is P:Q revenue in simplest form?
Answer 4:7
02 / UNDERSTAND & APPLY
A ratio compares two quantities; percentage change compares a difference with a specified starting quantity. A percentage-point change compares two percentages by subtraction. Choose the denominator before reaching for a calculator.
Because P starts lower, the same or even smaller absolute increase could produce a larger relative increase. Describing “faster growth” without defining absolute or percentage growth leaves ambiguity.
ORIGINAL WORKED EXAMPLE
Growth figure: From month 0 to month 3, find P’s increase in dollars and percentage increase.
Answer $30,000; 150%
ORIGINAL PRACTICE · 1
25%
Q rises by 15 thousand on a base of 60 thousand; 15/60=0.25=25%.
03 / UNDERSTAND & APPLY
Height answers “how much at this x?” Slope answers “how much change per unit of x?” Compare slopes using Δy/Δx in the same units and over explicitly defined intervals. Unequal horizontal intervals require division rather than comparing vertical rises alone.
At every plotted month Q’s revenue is higher, yet P gains $10,000 per month while Q gains $5,000 per month. This illustrates why a position and a rate are different targets.
ORIGINAL WORKED EXAMPLE
Growth figure: Complete two blanks. At month 2, the higher-revenue firm is [P/Q], and over months 0–3 the firm with greater average monthly dollar increase is [P/Q].
Answer Q; P
ORIGINAL PRACTICE · 1
$5,000 per month
P increases $10,000/month and Q $5,000/month. Their rate difference is $5,000/month, not the $25,000 revenue gap at month 3.
04 / UNDERSTAND & APPLY
An average of rates is valid without weighting only when the relevant denominators are equal. For a combined success rate, add successes and opportunities, then divide. Averaging displayed percentages gives equal weight to groups rather than to opportunities.
The original summary panel shows Small group: 20 attempts, 18 successes (90%); Large group: 80 attempts, 48 successes (60%). The labels provide the denominators needed for an overall calculation.
Full-size scientific diagram. Swipe or scroll horizontally; keyboard users can focus the diagram and use arrow keys.
ORIGINAL WORKED EXAMPLE
Summary panel: What is the combined success rate, and how far is it below the unweighted mean of group rates?
Answer 66%; 9 percentage points below
ORIGINAL PRACTICE · 1
0.66
The random unit is an attempt, so the favorable count is 66 out of 100. Giving each group equal selection probability would be a different experiment.
05 / UNDERSTAND & APPLY
For overlapping events, count their union by adding individual counts and subtracting the intersection once. For exactly one event, subtract the intersection twice from the sum of the individual counts. Complements are measured against the stated universe.
The original membership panel contains 100 people: 30 in A only, 20 in both A and B, 10 in B only and 40 in neither. Thus A has 50 members and B has 30. A person is selected uniformly from these 100 people in probability exercises.
ORIGINAL WORKED EXAMPLE
Membership panel: Find P(A or B) and P(B given A).
Answer 0.60; 0.40
ORIGINAL PRACTICE · 1
0.40
A only plus B only=30+10=40 of 100. The 20-person intersection is excluded.
ORIGINAL PRACTICE · 2
No
P(A)P(B)=0.50×0.30=0.15, whereas P(A and B)=20/100=0.20. Unequal values refute independence.
06 / UNDERSTAND & APPLY
A graph without exact labels may support an interval rather than a precise value. Preserve this uncertainty through the calculation. With positive quantities, a ratio’s minimum uses the smallest numerator and largest denominator; its maximum uses the largest numerator and smallest denominator.
For an explicitly bounded reading x∈[38,42] and y∈[68,72], x/y lies between 38/72≈0.528 and 42/68≈0.618. This proves x/y<0.7 but does not establish x/y=4/7. The illustrative bounds are separate from the exact growth dataset.
ORIGINAL PRACTICE · 1
Yes
The smallest possible ratio is 49/21≈2.333, already above 2. Every allowed pair satisfies the claim; a midpoint estimate is unnecessary.
07 / UNDERSTAND & APPLY
The observed growth rates do not prove future rates. If a question explicitly supplies linear continuation as a model, you may calculate its implications while labeling them predictions. Without that assumption, do not extend the graph to make a guaranteed statement.
Write units through intermediate work: thousands of dollars per month multiplied by months gives thousands of dollars. Convert only once at the end unless the response options use a different unit.
ORIGINAL PRACTICE · 1
At t=8 months, both $100,000
20+10t=60+5t gives 5t=40 and t=8; either formula gives 100 thousand. This is extrapolation beyond the observed months 0–3, conditional on the model.
08 / UNDERSTAND & APPLY
Dropdown choices constrain the allowed final response, but the two blanks may refer to different calculations. Record each blank’s quantity, unit and selected option. If one choice says “approximately,” estimate to the precision that distinguishes choices instead of manufacturing unnecessary decimal digits.
A complete answer to a two-blank question contains two selections. Do not let a correct first blank hide a wrong denominator, missing unit or unselected second blank.
ORIGINAL PRACTICE · 1
66; 40
The first uses 66 successes among 100 attempts, not the unweighted 75%. The second reads the 40-person outside region. Each blank has its own dataset and meaning.
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