Pipes & Cistern
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Quantitative Aptitude - Pipes & Cistern
Calculate filling and emptying rates accurately using combined work logic.
1. Concept
An inlet pipe fills and outlet pipe empties. Net rate = sum(inlet rates) − outlet rate.
2. Formula
If inlet fills in a days and b days, and outlet empties in c days: net rate = \(1/a + 1/b - 1/c\). Time to fill = \(1 / \text{net rate}\).
3. Quick Tips
- Convert times into rates (job/day) before combining.
- Sign matters: outflow reduces net rate.
4. Mistakes to Avoid
- Adding times instead of rates.
- Confusing inlet and outlet contributions.
5. Revision Checklist
- Practice inlet+outlet problems under time constraint.
Summary: Model pipes as work rates, combine correctly and solve for time with rate inversion.
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