Pipes & Cistern

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.