Unit 6 · Identifying Sufficient Information
Marble Box — Which Facts Are Sufficient?
Lesson 1 of 12
Identifying Sufficient Information questions test a precise analytical skill: knowing exactly what you need to know to solve a problem — no more, no less. The critical word is "sufficient" — does this information give one and only one answer?
This format appears consistently across OC TS tests and is a common source of mistakes because students confuse information that "helps" with information that "proves". An option can be useful and still not be sufficient.
The examiner wants to see whether you can set up the equation that needs to be satisfied and then test each option to check whether it produces exactly one unique numerical answer — not a range of possibilities, not multiple valid scenarios.
A total is given (e.g. 15 marbles across 3 types) and you must find which single piece of additional information lets you calculate a specific unknown with certainty. The correct option pins down all other variables with exact numbers.
Best approach: Write the equation: unknown = total − (everything else). Then test each option: does it give exact values for all remaining variables? If it only states a relationship ("more than", "twice as many") rather than a fixed count, it usually produces multiple valid combinations — which means it is not sufficient.
Question
A box contains only small, medium, and large marbles. There are 15 marbles in total.
Which one piece of information would be enough to work out exactly how many medium marbles there are?
Select an answer to see the explanation.
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