Quantitative Reasoning: Number Analogies, Series, Classification, and Inference
Quantitative Reasoning on the OLSAT covers number analogies, number series, number classification, and numeric inference. The arithmetic is usually simple; the difficulty is finding the rule and applying it consistently.
Core rules
- Number analogies: Express the first pair as an operation or relationship (multiply by 3, add 7, square). Apply the same operation to the third number. Check whether the rule is one-step or two-step.
- Number series: Find the difference between consecutive terms. If differences are not constant, look at second differences, ratios, alternating rules, or a pattern such as add 2, add 4, add 6.
- Number classification: Identify the number that does not share a property: prime/composite, square, multiple, even/odd, digit sum, or factor count.
- Numeric inference: Use given facts to deduce a missing value. Set up a simple relationship, keep units consistent, and check the answer against the original statement.
Worked example
3 : 9 :: 5 : ? The first pair multiplies by 3, so the answer is 15. Series: 2, 6, 12, 20, 30, ? Differences are 4, 6, 8, 10-increasing by 2. The next difference is 12, so the next term is 42.
Traps
- Assuming every series is arithmetic and stopping at the first difference.
- Applying a rule to the wrong term or reversing the analogy.
- Ignoring a two-step rule (add 3, then double).
- In classification, choosing a number because it "looks different" rather than testing a property.
- In inference, mixing units or answering a different question from the one asked.
Write the rule as an equation before computing; then test it on the second pair or term.