GMAT · Multi-Source Reasoning · TOPIC LESSON
Join sources only after matching their dates, units, definitions and populations.
BY THE END, YOU CAN
BEFORE YOU START
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LEARN THROUGH ORIGINAL PRACTICE
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01 / UNDERSTAND & APPLY
Multi-Source Reasoning presents a shared source set, potentially supporting more than one question. Map each tab by function: definitions, raw data, policy, update or interpretation. A map saves rereading without requiring you to memorize every number.
The original three-source set below is fictional. The figure keeps its unit and time differences visible. Use these sources for all questions labeled “May/June set” in this lesson.
Source 1 — Dispatch ledger, May only: Aster shipped 40 cartons, Birch 30 cartons and Cedar 50 cartons. Every carton contained 12 units. These are gross shipments, before returns.
Source 2 — Returns ledger, same May shipments: Aster had 24 units returned, Birch 36 and Cedar 0. All other shipped units were accepted. For this exercise, net accepted units = gross shipped units − returned units.
Source 3 — Operations memo: the June plan is Aster 45 cartons, Birch 35 and Cedar 50, each still containing 12 units. The memo calls the May network acceptance rate “above 95%.” June quantities are plans, not completed shipments.
Full-size scientific diagram. Swipe or scroll horizontally; keyboard users can focus the diagram and use arrow keys.
ORIGINAL WORKED EXAMPLE
May/June set: What is Aster’s net accepted May quantity?
Answer 456 units
02 / UNDERSTAND & APPLY
A shared name is a join key only if its meaning and scope agree across sources. Match depot, month, product and measurement basis before combining values. A table row for May shipments does not automatically match a June forecast for the same depot.
Write the join explicitly: depot + May shipments links dispatch to returns. Units per carton then converts the dispatch count into the unit used by the return ledger. This prevents subtracting 24 units from 40 cartons.
ORIGINAL WORKED EXAMPLE
May/June set: What was the network’s total net accepted May quantity?
Answer 1,380 units
ORIGINAL PRACTICE · 1
324 units
Birch gross=30×12=360. Subtract its 36 returned units to obtain 324.
ORIGINAL PRACTICE · 2
540 units
Source 3 specifies 45 cartons, each containing 12 units. Planned units=45×12=540; this is not evidence that 540 were actually accepted.
03 / UNDERSTAND & APPLY
A comparison is meaningful only when its denominator and population are matched. Total returns divided by total shipped units measures a network rate. An average of depot rates instead gives each depot equal weight, regardless of its size.
Do not treat a reporting-date mismatch as an automatic contradiction. A plan can differ from an earlier actual count; gross shipments can exceed net accepted units; a subgroup percentage can differ from the whole. First ask whether both claims concern the same thing.
ORIGINAL WORKED EXAMPLE
May/June set: Is the memo’s “above 95%” description of May network acceptance supported?
Answer Yes, supported
ORIGINAL PRACTICE · 1
No
Depot rates are 456/480=95%, 324/360=90% and 600/600=100%. Their unweighted mean is 95%, whereas the shipment-weighted network rate is about 95.83%.
04 / UNDERSTAND & APPLY
For every conclusion, name the source facts and the logical bridge. A sentence in a memo may be a claim to evaluate rather than a fact that overrides the table. If the task asks whether the claim follows, verify it using the defined quantities.
The strength of the requested conclusion matters. “Can be consistent with” needs a compatible interpretation; “must follow” needs support in all allowed interpretations. Do not substitute a plausible operational story for missing evidence.
ORIGINAL WORKED EXAMPLE
May/June set: Select Supported or Not supported for each of two rows: (i) Cedar supplied more than 40% of May net accepted units; (ii) Cedar will certainly supply 600 net accepted units in June.
Answer (i) Supported; (ii) Not supported
ORIGINAL PRACTICE · 1
Source 1 only
The dispatch count of 50 cartons and 12 units per carton fixes 600 gross units. Returns and future plans are unnecessary.
05 / UNDERSTAND & APPLY
Claims contradict only if they cannot both be true under the same relevant definitions and conditions. “Aster shipped 40 cartons in May” and “Aster plans 45 in June” can both be true. A claim that May gross shipments were exactly 500 units cannot agree with 40 cartons of 12 units.
When definitions are absent, the correct conclusion may be that reconciliation is unresolved. Do not manufacture a change in units or dates solely to rescue inconsistent evidence.
ORIGINAL WORKED EXAMPLE
May/June set: An additional note says Birch’s gross May shipments were exactly 400 units. Is it compatible with Source 1 as written?
Answer No; it contradicts Source 1
ORIGINAL PRACTICE · 1
No
They describe different months and different statuses, planned versus actual. A difference in value is not by itself a contradiction.
06 / UNDERSTAND & APPLY
An apparently irrelevant memo may contain a definition or exception needed to interpret another tab. Conversely, a vivid narrative detail can be irrelevant even when it concerns the same organization. Relevance is determined by the question’s target.
For a simple May net count, June plans can be ignored. For a planned growth comparison, the June tab becomes essential. Reuse your map, but update which sources are needed for each question.
ORIGINAL PRACTICE · 1
8⅓%
June plan totals 45+35+50=130 cartons. May totals 120. Increase/May base=10/120=1/12=8⅓%. Return data do not affect carton shipment counts.
ORIGINAL PRACTICE · 2
No
The rates are 36/360=10% and 24/480=5%, but no evidence identifies a cause. Greater rate is a numeric comparison, not a causal explanation.
07 / UNDERSTAND & APPLY
Words such as planned, confirmed, estimated, at least and subject to alter what a source can establish. If a rule applies only to confirmed orders, a forecast is not enough to trigger it. If a source says exactly, do not silently soften it to approximately.
One question can ask for several binary judgments. Decide each directly from the sources; do not force the answers into a pattern or assume the interface must contain a certain number of yes responses.
ORIGINAL PRACTICE · 1
(i) Supported; (ii) Supported
Net counts are Aster 456, Birch 324 and Cedar 600. Cedar is largest; 456−324=132. Both independently follow.
08 / UNDERSTAND & APPLY
For each answer, state target → source values → unit conversion → rule or operation → conclusion. If any arrow requires an unstated assumption, weaken the conclusion or look for another source.
This method scales from tables and emails to graphs and policies: keep definitions near the values they control, preserve the shared-source set, and treat each actual question as a new reasoning task.
KEEP THE BIG IDEAS
READ WITH CONTEXT
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