The three topics that appear in every placement paper — and the mental-math shortcuts that turn a 90-second problem into a 20-second one.
Percentages, ratios and averages show up in every aptitude paper, often disguised inside data-interpretation sets. Speed here frees up time for harder questions elsewhere.
Percentages
- Memorise fraction equivalents:
1/8 = 12.5%,1/6 ≈ 16.67%,1/3 ≈ 33.33%. Conversions become instant. - Successive percentage change of a% then b% equals
a + b + (ab/100). A 20% rise then 20% fall is a net 4% loss, not zero.
Ratios
- Scale a ratio to a known total before computing parts.
- When two ratios share a term, cross-multiply to combine them into one chain.
Averages
- Use the deviation method: pick an assumed mean, average the small deviations, add back. Much faster than summing large numbers.
- Weighted averages: the answer always sits between the two group averages, closer to the larger group.
Practise the recognition, not just the formula
The real skill is spotting which shortcut a question wants in the first two seconds. Drill mixed sets — not one topic at a time — so your brain learns to switch. The prephasz Quick Aptitude drills are built exactly this way.
Put this into practice
Drill these exact patterns with adaptive practice, timed mocks and company-wise assessments on prephasz.
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