# GMAT Multi-Source Reasoning: Rules and Exceptions | topin

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## Treat source selection as an applicability question

GMAC’s Multi-Source Reasoning description includes recognising discrepancies, making inferences and judging relevant data. The tabs below are original teaching material. The [general Multi-Source guide](/gmat/data-insights/multi-source-reasoning) covers navigation; this article concentrates on reconciling rules with different dates and scopes.

For each rule, extract four fields: who or what it applies to, when it applies, the required action and any exception. A newer memo about express orders may not change standard orders. A trial in one region may not change the national policy. Dates alone do not establish which rule wins.

Then connect the question to a transaction. Identify its date, category and relevant status. Only after that should you calculate a charge or mark a claim. This order prevents accurate arithmetic using an inapplicable rule. Most of the useful work is deciding which conditions the row actually satisfies.

If two sources seem inconsistent, look for an explicit update, restricted scope or changed definition. Do not invent a hierarchy such as “email always overrides policy”. A question can ask you to identify an unresolved discrepancy rather than forcing you to resolve it through an unstated rule.

## Original three-tab policy set

Tab A, published 1 September: a distributor charges £6 handling per order. Express service adds £5\. Orders weighing more than 4 kg add £3\. The weight threshold is strict: exactly 4 kg does not attract the supplement. These charges apply unless a later stated policy changes them.

Tab B, update effective 10 October: for express orders placed after 15:00 on Fridays, dispatch changes to standard and the express supplement is removed. The weight supplement remains. The update does not affect orders placed at 15:00 exactly. No other dispatch or fee rules change.

__Tab C: invented order records__
| Order  | Date and weekday    | Time  | Weight | Selected service |
| ------ | ------------------- | ----- | ------ | ---------------- |
| Cedar  | Friday 9 October    | 16:00 | 5 kg   | Express          |
| Maple  | Friday 16 October   | 15:30 | 5 kg   | Express          |
| Willow | Friday 16 October   | 15:00 | 4 kg   | Express          |
| Birch  | Saturday 17 October | 16:00 | 5 kg   | Express          |

Question: which orders lose the express supplement under the update? Only Maple meets all three conditions: after the effective date, on a Friday and after 15:00\. Cedar is earlier than the update; Willow is at the excluded boundary; Birch is not Friday. Reading only the times would incorrectly include Cedar and Birch.

## Carry the applicable rule into the fee calculation

Cedar remains under the earlier arrangement: £6 + £5 + £3 = £14\. Maple loses the express supplement but keeps the weight supplement: £6 + £3 = £9\. Willow retains express and has no weight supplement: £6 + £5 = £11\. Birch retains both supplements: £14\. Total handling is £48.

A total of £43 would remove Cedar’s express supplement before the update took effect. A total of £38 would also remove Birch’s supplement despite its Saturday date. A total of £45 could miss a weight supplement. These original distractor analyses show why tagging an incorrect total as “arithmetic” may conceal a policy-selection mistake.

Create a compact fee decomposition rather than a large copied table: base, express and weight. Once you know which rule applies, the calculation is simple. If a later question asks about dispatch rather than money, reuse the applicability result but check the different requested output.

Do not carry an answer from one question into another without verifying its scope. “Maple pays less” does not automatically mean “Maple arrives first”, because the tabs define charges and dispatch conversion, not complete arrival outcomes. Our [RC inference guide](/articles/gmat-rc-inference-scope) develops the related discipline of keeping conclusions within available evidence.

## Check effective dates and strict inequalities explicitly

Write “after 15:00” as time > 15:00, and “more than 4 kg” as weight > 4\. Exactly 15:00 and exactly 4 kg fail those strict tests. If the prompt instead used “at or after” or “at least”, the boundary rows would change. A familiar everyday interpretation should not erase the wording.

For a second original variation, suppose the update is effective for orders dispatched after 10 October rather than orders placed after that date. A 9 October placement dispatched later may now be affected. The event associated with the date matters as much as the date itself. Keep “placed” and “dispatched” in separate fields.

For another variation, the memo applies only to retail customers. A business-customer order meeting the same date and time criteria remains outside that update unless the source says otherwise. Do not expand an exception to all rows because it seems operationally sensible.

These variations make good transfer exercises. Change one phrase and predict which row changes before recalculating the total. If you cannot isolate the affected row, you probably have not represented the applicability rule precisely enough. The exercise tests reading and logic more than calculation speed.

## Distinguish contradiction, update and missing information

A contradiction occurs when sources make incompatible claims about the same case under the same conditions. An update changes the rule for a defined later scope. Missing information leaves a question unresolved. These three situations require different responses, so label them before choosing a conclusion.

Original example: one tab says all express orders after 15:00 are standard; another says Friday express orders after 15:00 are standard from 10 October. Without knowing whether the first is a current general policy, an earlier policy or a summary, you should not automatically infer that all non-Friday orders change. Inspect the source headings and instructions.

Original missing-data example: an order lists “express” and 5 kg but gives no placement time. Under the October Friday exception, you may know the base and weight charge yet not whether the express supplement applies. The total could be £9 or £14\. Calculating a unique figure would silently assume the missing time.

That resembles [yes/no Data Sufficiency](/articles/gmat-data-sufficiency-yes-no): multiple allowed cases can defeat a determinate judgment. However, follow the MSR question’s actual response labels. Do not force a Data Sufficiency letter onto an MSR statement asking whether a conclusion is supported.

Original two-rule variation: Tab A says business customers get a £2 handling reduction, and Tab B removes the express supplement for qualifying Friday orders. If a qualifying business order weighs 5 kg, and the sources say the reduction applies to the base handling charge, its fee is (£6 − £2) + £3 = £7\. Both rules can apply because neither is stated to cancel the other.

If the reduction instead applies only to orders retaining express service, the same order may not qualify after its dispatch changes to standard. That altered condition changes the result even though the figures stay the same. Read whether eligibility depends on the selected service, final service or customer category.

Keep mutually compatible rules separate from genuine contradictions. A discount and a supplement can coexist; a general rule and a scoped exception can coexist; two incompatible claims about the same final charge may require a discrepancy judgment. The tab’s date is one clue, not a universal sorting algorithm for truth.

## Review source mistakes using a row-level evidence trail

For each response, record the source and condition that justify it. “Maple: B effective date and Friday time; C row supplies facts” is enough. This evidence trail makes an error review concrete. If you choose the wrong fee, you can identify whether the mistake was the source, scope, boundary or arithmetic.

During a timed set, map the tabs briefly and return for relevant details rather than memorising every row. A rule-heavy question often rewards a short condition list more than a long narrative summary. Keep unrelated source details available without spending time copying them into notes.

If a multi-part item includes three claims, check each independently against the sources. Correctly solving the total fee does not establish a claim about delivery priority or customer eligibility. Treat multi-part items as all-or-nothing, as most prep providers report: one unchecked claim can cost the whole question.

topin’s [free full-length GMAT mock](/gmat/practice-test), marked on the official scale, can test navigation and applicability within a complete DI section. Use this worked set to learn the process, then verify it on unfamiliar tabs. A memorised total of £48 tells you little about whether you can identify the right rule in a new situation.

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## FAQs

Does the newest tab always override older tabs?

No. Check effective date, population and scope. A newer restricted update may leave other cases under the earlier rule.

How should I handle “after” and “more than”?

Treat them as strict conditions unless the prompt says otherwise. Exactly equal values do not satisfy them.

Can one correct calculation answer every question in an MSR set?

No. Later questions may ask different outputs or populations. Reuse relevant work while checking each requested claim.

What if a transaction time is missing?

Consider the allowed cases. If different times produce different outcomes, a unique result may not be supported.

What should I record after an MSR error?

Name the source, applicability condition and row you used, then label the failure as scope, date, boundary, lookup or calculation.

## Sources (checked 5 October 2026)

* [mba.com: MSR discrepancies and relevance (checked 5 October 2026)](https://www.mba.com/exams/gmat-exam/about/exam-content)

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